Passive infra-red detectors

ABSTRACT

A passive infra-red detector including at least three sub-detectors, each sub-detector being operative to receive infra-red radiation from a corresponding one of at least three sub fields-of-view, each sub field-of-view being exclusively defined by an optical element which does not define any other sub field of view, the sub fields-of-view being angled with respect to each other, adjacent ones of the sub fields-of-view being separated by a gap of no more than 30 degrees and at least one of the sub fields-of-view having at least one of the following characteristics: extending over no more then 45 degrees in azimuth; and including not more than three azimuthally distributed detection zones, and signal processing circuitry, operative to receive output signals from the sub detectors and to provide a motion detection output.

CROSS-REFERENCE TO PRIOR APPLICATION

This is a continuation of U.S. patent application Ser. No. 10/596,695,filed on Jun. 21, 2006, which is the U.S. National Phase ofInternational Patent Application PCT/IL2006/000356, filed Mar. 20, 2006,which claims priority from U.S. Provisional Application No. 60/664,231,filed Mar. 21, 2005.

REFERENCE TO RELATED APPLICATIONS

Reference is made to U.S. Provisional Patent Application No. 60/664,231,entitled PASSIVE INFRA-RED DETECTORS AND TECHNIQUES EMPLOYINGSUB-DETECTORS, filed Mar. 21, 2005, the disclosure of which is herebyincorporated by reference and priority of which is hereby claimedpursuant to 37 CFR 1.78(a) (4) and (5)(i).

FIELD OF THE INVENTION

The present invention relates to passive infrared detectors generally.

BACKGROUND OF THE INVENTION

Passive infrared detectors known in the art have an optical design whichis usually based on the use of multiple optical elements, such as lensor mirror segments, arranged in one or more rows, each row including oneor more segments. The segments within the rows are arranged with theiroptical axes spread azimuthally in a plane, generally parallel to thehorizontal, or inclined with respect to the horizontal. Each of thesegments is arranged to focus IR energy emanating from a pre-defineddetection zone onto an infrared sensor such as a pyroelectric sensor,which is common to multiple segments. The combined detection zones ofthe multiple optical elements or segments, constitute the field-of-viewof the detector, which is defined as the detection region covered by thedetector or the “coverage” of the detector.

A commercially successful prior art detector is the Coral Plus detector,commercially available from Visonic Ltd. of Israel. This detectorincludes a lens assembly and a dual element pyroelectric sensor,comprising a pair of sensor elements. The pyroelectric sensor employedin this detector is a Perkin-Elmer LHi-968 dual element sensor. The lensassembly includes multiple Fresnel lens segments arranged in three rows,which are positioned in front of the sensor and serve as a detectorwindow. Other prior art lens assemblies comprise only two rows ofoptical segments, an upper row, including Fresnel lens segments, and alower row, including cylindrical optical segments.

A person moving through the field-of-view of the detector causesgeneration of a signal output from the sensor. This signal is defined tobe a “desired signal”. Signal processing circuitry of the detectordetects and processes the desired signal and activates an alarm signaloutput.

There are also known detectors which operate similarly to the lens-baseddetectors described hereinabove but employ mirror segments rather thanlens segments. In such detectors, incoming infrared radiation enters thedetector through a wide IR transparent window in the detector housingand is reflected by the mirror segments to focus onto a pyroelectricsensor. The window is provided to prevent insects and other spuriousmatter from entering the detector. In lens-based detectors of the typedescribed hereinabove, the lens itself also functions as a window.

The prior art detectors described hereinabove, whether lens-based,mirror-based or employing both lenses and mirrors, are particularlysuitable for indoor applications. However, when installed outdoors or inharsh environments, such detectors are subject to operational conditionsof various types, which cause false alarms. These conditions mayinclude, but are not limited to:

Wind bursts which produce flows of hot or cold air onto and into thedetector and cause a change in the temperatures of various elements ofthe detector, such as the housing, the window or the sensor.

Rain and snow which cause changes in the temperature of the backgroundas well as changes in the temperature of the housing and the window.These effects are amplified when the detector is also subject to wind.

Extreme environmental conditions and extreme changes thereof which causesignificant thermal interference signals.

Large variations in temperature within the field-of-view. For instance,a black asphalt road that is exposed to the sun can reach temperaturesas high as 50° C.-60° C. while a nearby pool or irrigated grass can havetemperatures as low as 15° C. In such cases, a moving person having atemperature of 35° C.-37° C. will differ from the background by over+20° C. with respect to the irrigated grass and −15° C. with respect tothe asphalt road.

-   -   Movement of background elements in the field-of-view.    -   Fast changes in background temperature within the field-of-view.    -   High level of sunlight radiation.    -   Presence of animals, such as pets and rodents.

In prior art PIR detectors, the pyroelectric sensor receives not only“desired signals” but also simultaneously receives undesired thermalinterference signals (“undesired signals”) emanating concurrently fromwithin the field-of-view.

Thus, for example, if a detector, having nine lens or mirror segments ina horizontal row which define nine detection zones, is designed todetect “desired signals” emanating from a single detection zone at agiven moment in time, it actually receives at the same time also“undesired signals” emanating concurrently from the eight remainingdetection zones. The “undesired signals” result from temperaturevariations at the wide detector window and the housing, air drafts,moving trees and bushes, animals and other sources as described above.

Accordingly, in this example, the total level of the “undesired signals”(interference) to which the detector is exposed, is about nine timeslarger than the “desired signal” emanating from a single zone. In manycases, especially in outdoor environments, the total level of the“undesired signals” may be even larger than that of the “desired signal”which the detector is designed to detect. This is the main reason forthe many false alarms in outdoor environments.

Various solutions have been proposed for outdoor applications bymanufacturers such as Optex Co. Ltd. of Japan, Crow ElectronicEngineering Ltd. of Israel, and Paradox Security Systems Ltd. of Canada.Generally, the proposed solutions incorporate two sensors, havinggenerally overlapping fields-of-view, into the same detector housing toactivate a common alarm output upon generally simultaneous detection ofmotion by both sensors. Prevention of false alarms is based on thestatistical assumption that the probability that each of the two sensorswill generate a false alarm at approximately the same instant is verylow. On the other hand, inasmuch as both detectors have more or less thesame field-of-view, detection processing is based on detecting a“desired signal” in both sensors at approximately the same time.Although such detectors perform better outdoors than a detectoremploying a single sensor, they still do not provide sufficientlyreliable detection, because much of the interference existing outdoors,as explained hereinabove, generates “undesired signals” simultaneouslyin both sensors, due inter-alia, to the fact that both sensors view thesame field-of-view.

The following published patent documents and other publications arebelieved to represent the current state of the art:

U.S. Pat. Nos.: 3,524,180; 3,958,118; 4,058,726; 4,081,680; 4,087,688;4,271,359; 4,375,034; 4,479,056; 4,604,524; 4,614,938; 4,645,930;4,704,533; 4,709,152; 4,912,748; 4,943,800; 5,296,707; 5,559,496;5,693,943; 5,703,368; 5,844,240; 6,150,658; 6,163,025 and 6,211,522.

Product sheets of known outdoor detectors on the market:

-   -   Optex Co. Ltd.—models LX-402/802N and VX-402/402R/402REC. Model        VX-402/402R/402REC is described in U.S. Pat. No. 5,703,368.    -   Crow Electronic Engineering Ltd.—D&D (Daredevil) and MRX-300.        The MRX-300 incorporates a micro-wave detector.    -   Paradox Security Systems Ltd.—Digigard DG85.

SUMMARY OF THE INVENTION

A principal objective of the present invention is to manage interferenceand substantially decrease the “undesired signals” detected by a sensor,and as a result to increase the ratio between the “desired signal” andthe “undesired signals”, arising from interference, at every point intime. An additional objective of the invention is to provide improvedsignal processing to enable the detector to better distinguish betweenthe “desired signals” and the “undesired signals”. A further objectiveof the invention is to provide an improved optical mechanical designthat performs better and is more immune to false alarms.

There is thus provided in accordance with a preferred embodiment of thepresent invention a passive infra-red detector including at least threesub-detectors, each of the at least three sub-detectors being operativeto receive infra-red radiation from a corresponding one of at leastthree sub fields-of-view, each of the at least three sub fields-of-viewbeing exclusively defined by an optical element which does not defineany other of the at least three sub fields of view, the at least threesub fields-of-view being angled with respect to each other, adjacentones of the at least three sub fields-of-view being separated by a gapof no more than 30 degrees and at least one of the at least three subfields-of-view having at least one of the following characteristics:extending over no more then 45 degrees in azimuth; and including notmore than three azimuthally distributed detection zones, and signalprocessing circuitry, operative to receive output signals from the atleast three sub detectors and to provide a motion detection output.

In accordance with a preferred embodiment of the present invention theat least three sub fields-of-view are substantially non-overlapping.Preferably, each optical element is directed in a correspondingdirection, the corresponding directions of the optical elements of eachtwo of the at least three sub-detectors being different.

In accordance with another preferred embodiment of the present inventionthe optical element includes a non focusing optical element. Preferably,the non-focusing optical element includes a reflective optical element.Additionally or alternatively, the optical element includes a focusingelement. Preferably, the focusing element includes at least one of areflective element, a refractive element, a diffractive element and acylindrical optical element.

In accordance with yet another preferred embodiment of the presentinvention the azimuthally distributed detection zones have correspondingdivergence angles and the gap has an angular extent which is less thanor equal to twice the largest angular extent of the divergence angles ofdetection zones of the adjacent ones of the at least three subfields-of-view. Alternatively, the gap has an angular extent which isless than or equal to a largest azimuthal angle A-2B between any twoadjacent detection zones of the adjacent ones of the at least three subfields-of-view.

There is also provided in accordance with another preferred embodimentof the present invention a passive infra-red detector including at leastthree sub-detectors, each operative to receive infra-red radiation froma corresponding one of at least three sub fields-of-view and signalprocessing circuitry, receiving output signals from at least two of theat least three sub-detectors and providing a motion detection output inresponse to receipt of the output signals; noting, within apredetermined first time period, multiple detections by one of the atleast two sub-detectors and the absence of detections by another of theat least two sub-detectors and being operative to ignore futuredetections by the one of the at least two sub-detectors for at least apredetermined second time period.

In accordance with a preferred embodiment of the present invention, theat least three sub fields-of-view are substantially non-overlapping.Preferably, the signal processing circuitry is operative to ignore thefuture detections only in a case where the multiple detections fulfillpredetermined pre-alarm criteria.

In accordance with a further preferred embodiment of the presentinvention the signal processing circuitry is operative to ignore thefuture detections only in a case where the multiple detections fulfillpredetermined alarm criteria. Additionally or alternatively, the signalprocessing circuitry is operative to extend the predetermined secondtime period in response to detections by the one of the at least twosub-detectors during the predetermined second time period.

In accordance with yet a further preferred embodiment of the presentinvention the signal processing circuitry is operative to note asequence of receipt of the output signals by the at least threesub-detectors and to provide motion direction output based on thesequence. Additionally or alternatively, the signal processing circuitryis operative to note a sequence of receipt of the output signals by theat least three sub-detectors and to provide motion path outputinformation based on the sequence.

In accordance with a still further preferred embodiment of the presentinvention the signal processing circuitry is operative to process theoutput signals according to at least one predefined criterion.Preferably, the at least one predefined criterion includes whether atime duration between receipt of the output signals from adjacent onesof the at least three sub-detectors lies within a predetermined range ofvalues.

In accordance with yet another preferred embodiment of the presentinvention the signal processing circuitry is operative to process theoutput signals according to the at least one predefined criterion bynoting time durations of the output signals from adjacent ones of the atleast three sub-detectors and providing the motion detection output atleast when the ratio between the time durations is within certainlimits. Preferably, the ratio is in the range of 0.5 to 2.0.

In accordance with still another preferred embodiment of the presentinvention, the signal processing circuitry is operative to process theoutput signals according to the at least one predefined criterion bynoting a time difference between receipt of the output signals and timedurations of the output signals and to provide the motion detectionoutput in response to receipt of the output signals from at least twoadjacent ones of the at least three sub-detectors having respective timedurations and a time difference therebetween, the time durations and thetime difference therebetween having a time relationship therebetweenwhich meets at least one predetermined criterion.

In accordance with an additional preferred embodiment of the presentinvention the at least one predetermined criterion includes whether aratio between the time difference and at least one of the time durationslies within a predetermined range of values. Alternatively oradditionally, the at least one predetermined criterion includes whetherratios between the time difference and each of the time durations liewithin a predetermined range of values. Preferably, the predeterminedrange of values is based at least in part on divergence angles of atleast two zones of two different ones of the at least three subfields-of-view corresponding to the at least two adjacent ones of the atleast three sub-detectors. Alternatively, the predetermined range ofvalues is based at least in part on an angle between of at least twozones of two different ones of the at least three sub fields-of-viewcorresponding to the at least two adjacent ones of the at least threesub-detectors.

In accordance with another preferred embodiment of the present inventionthe passive infra-red detector is operative to receive radiation from afield-of-view having a field-of-view divergence angle of at least 45degrees. Preferably, at least one of the at least three subfields-of-view includes a single coplanar azimuthally distributeddetection zone. Additionally or alternatively, at least one of the atleast three sub fields-of-view includes multiple coplanar azimuthallydistributed detection zones.

In accordance with yet another preferred embodiment of the presentinvention at least one of the at least three sub fields-of-view includesa single vertically distributed detection zone. Additionally oralternatively, at least one of the at least three sub fields-of-viewincludes multiple vertically distributed detection zones.

In accordance with still another preferred embodiment of the presentinvention the passive infra-red detector also includes a housing formedwith an aperture adapted for passage therethrough of infra-redradiation, wherein the at least three sub fields-of-view intersectgenerally at an intersection region located at the aperture, and theaperture is generally equal in size to the size of the intersectionregion. Preferably, a window transparent to infra-red radiation islocated adjacent the aperture.

In accordance with a further preferred embodiment of the presentinvention a center of the window is located generally at a center of theaperture. Preferably, the window has a circular cross-section.Alternatively, the window is generally flat. Preferably, the window isformed of at least one of HDPE, Silicon and Germanium.

In accordance with another further preferred embodiment of the presentinvention the passive infra-red detector also includes masking detectionfunctionality for providing an alarm output upon detection of maskingmaterials obstructing the window. Preferably, the passive infra-reddetector also includes a guard element surrounding the window forproviding mechanical protection to the window.

There is further provided in accordance with yet another preferredembodiment of the present invention a passive infra-red detectorincluding at least three sub-detectors, each of the at least threesub-detectors being operative to receive infra-red radiation from acorresponding one of at least three sub fields-of-view, each of the atleast three sub fields-of-view being exclusively defined by an opticalelement which does not define any other of the at least three sub fieldsof view, the at least three sub fields-of-view being angled with respectto each other and reduced false alarm signal processing circuitry,receiving output signals from the at least three sub-detectors andproviding a motion detection output and being operative to eliminate atleast some false alarms at least based on sensed time relationshipsbetween the output signals.

In accordance with a preferred embodiment of the present invention theat least three sub fields-of-view are substantially non-overlapping.Preferably, the signal processing circuitry is operative to process theoutput signals by noting time durations of the output signals fromadjacent ones of the at least three sub-detectors and providing themotion detection output at least when the ratio between the timedurations is within a predetermined range of values. More preferably,the predetermined range of values is 0.5 to 2.0.

In accordance with another preferred embodiment of the present inventionthe signal processing circuitry is operative to process the outputsignals by noting a time difference between receipt of the outputsignals and time durations of the output signals and to provide themotion detection output if, in response to receipt of the output signalsfrom at least two adjacent ones of the at least three sub-detectorshaving respective time durations and a time difference therebetween, thetime durations and the time difference therebetween having a timerelationship therebetween which meets at least one predeterminedcriterion.

In accordance with yet another preferred embodiment of the presentinvention the at least one predetermined criterion includes whether aratio between the time difference and at least one of the time durationslies within a predetermined range of values. Additionally oralternatively, the at least one predetermined criterion includes whetherratios between the time difference and each of the time durations liewithin a predetermined range of values. Preferably, the predeterminedrange of values is based at least in part on divergence angles of atleast two zones of two different ones of the at least three subfields-of-view corresponding to the at least two adjacent ones of the atleast three sub-detectors. Alternatively, the predetermined range ofvalues is based at least in part on an angle between at least two zonesof two different ones of the at least three sub fields-of-viewcorresponding to the at least two adjacent ones of the at least threesub-detectors.

In accordance with still another preferred embodiment of the presentinvention each optical element is directed in a corresponding direction,the corresponding directions of the optical elements of each two of theat least three sub-detectors being different.

In accordance with a further preferred embodiment of the presentinvention the optical element includes a non-focusing optical element.More preferably, the non-focusing optical element includes a reflectiveoptical element. Alternatively, the optical element includes a focusingelement. Preferably, the focusing element includes at least one of areflective element, a refractive element, a diffractive element and acylindrical optical element.

There is still further provided in accordance with another preferredembodiment of the present invention a passive infra-red detectorincluding at least three sub-detectors, each operative to receiveinfra-red radiation from a corresponding one of at least three subfields-of-view, the at least three sub fields-of-view beingsubstantially non-overlapping and being angled with respect to eachother and signal processing circuitry, receiving output signals from theat least three sub-detectors and noting time differences between receiptof the output signals from adjacent ones of the at least threesub-detectors and providing a motion detection output in response toreceipt of the output signals from the adjacent ones of the at leastthree sub-detectors having a time difference which is at least withincertain predetermined limits.

There is yet further provided in accordance with yet a further preferredembodiment of the present invention a passive infra-red detectorincluding at least three sub-detectors, each operative to receiveinfra-red radiation from a corresponding one of at least three subfields-of-view, the at least three sub fields-of-view being angled withrespect to each other and signal processing circuitry, receiving outputsignals from at least two adjacent ones of the at least threesub-detectors, noting time durations of the output signals and providinga motion detection output in response to receipt of the output signalsfrom the at least two adjacent ones of the at least three sub-detectorshaving respective time durations, the ratio of which is withinpredetermined limits.

In accordance with a preferred embodiment of the present invention theat least three sub fields-of-view are substantially non-overlapping.Preferably, the ratio is within the range of 0.5 to 2.0.

There is additionally provided in accordance with another preferredembodiment of the present invention a passive infra-red detectorincluding at least three sub-detectors, each operative to receiveinfra-red radiation from a corresponding one of at least three subfields-of-view, the at least three sub fields-of-view being angled withrespect to each other and signal processing circuitry, receiving outputsignals from at least two adjacent ones of the at least threesub-detectors, noting time differences between receipt of the outputsignals and time durations of the output signals and providing a motiondetection output in response to receipt of the output signals from atleast two adjacent ones of the at least three sub-detectors havingrespective time durations and a time difference therebetween, the timedurations and the time difference therebetween having a timerelationship therebetween which meets at least one predeterminedcriterion.

In accordance with a preferred embodiment of the present invention, theat least three sub fields-of-view are substantially non-overlapping.Preferably, the at least one predetermined criterion includes whether aratio between the time difference and at least one of the time durationslies within a predetermined range of values. Alternatively, the at leastone predetermined criterion includes whether ratios between the timedifference and each of the time durations lie within a predeterminedrange of values.

In accordance with another preferred embodiment of the present inventionthe predetermined range of values is based at least in part ondivergence angles of at least two zones of two different ones of the atleast three sub fields-of-view corresponding to the at least twoadjacent ones of the at least three sub-detectors. Additionally oralternatively, the predetermined range of values is based at least inpart on an angle between at least two zones of two different ones of theat least three sub fields-of-view corresponding to the at least twoadjacent ones of the at least three sub-detectors.

In accordance with another preferred embodiment of the present inventionthe signal processing circuitry is operative to note a sequence ofreceipt of the output signals by the at least three sub-detectors and toprovide motion direction output based on the sequence. Alternatively,the signal processing circuitry is operative to note a sequence ofreceipt of the output signals by the at least three sub-detectors and toprovide motion path output information based on the sequence.Preferably, the passive infra-red detector is operative to receiveradiation from a field-of-view having a field-of-view divergence angleof at least 45 degrees.

In accordance with yet another preferred embodiment of the presentinvention at least one of the at least three sub fields-of-view includesa single coplanar azimuthally distributed detection zone. Alternatively,at least one of the at least three sub fields-of-view includes multiplecoplanar azimuthally distributed detection zones.

In accordance with still another preferred embodiment of the presentinvention at least one of the at least three sub fields-of-view includesa single vertically distributed detection zone. Alternatively, at leastone of the at least three sub fields-of-view includes multiplevertically distributed detection zones.

In accordance with a further preferred embodiment of the presentinvention adjacent ones of the at least three sub fields-of-view areseparated by a gap of no more than 30 degrees. Preferably, theazimuthally distributed detection zones have corresponding divergenceangles and the gap has an angular extent which is less than or equal totwice the largest angular extent of the divergence angles of detectionzones of the adjacent ones of the at least three sub fields-of-view.Additionally or alternatively, the gap has an angular extent which isless than or equal to a largest azimuthal angle A-2B between any twoadjacent detection zones of the adjacent ones of the at least three subfields-of-view.

In accordance with another further preferred embodiment of the presentinvention the passive infra-red detector also includes a housing formedwith an aperture adapted for passage therethrough of infra-redradiation, wherein the at least three sub fields-of-view intersectgenerally at an intersection region located at the aperture, and theaperture is generally equal in size to the size of the intersectionregion.

In accordance with yet a further preferred embodiment of the presentinvention a window transparent to infra-red radiation is locatedadjacent the aperture. Preferably, a center of the window is locatedgenerally at a center of the aperture.

In accordance with still a further preferred embodiment of the presentinvention the window has a circular cross-section. Alternatively, thewindow is generally flat. Preferably, the window is formed of at leastone of HDPE, Silicon and Germanium.

In accordance with another preferred embodiment of the present inventionthe passive infra-red detector also includes masking detectionfunctionality for providing an alarm output upon detection of maskingmaterials obstructing the window. Preferably, the passive infra-reddetector also includes a guard element surrounding the window forproviding mechanical protection to the window.

There is also provided in accordance with another preferred embodimentof the present invention a passive infra-red detector having afield-of-view including multiple detection zones, the detector includinga housing having an aperture for passage of infra-red radiationtherethrough, at least one sensor disposed in the housing and at leastone infra-red radiation director including a plurality of infra-redoptical elements each associated with a different one of the multipledetection zones, each of the plurality of infra-red optical elementsbeing operative to receive infra-red radiation from a corresponding oneof the multiple detection zones and to direct the infra-red radiation tothe at least one sensor along a corresponding radiation path, aplurality of the radiation paths generally intersecting at anintersection region located at the aperture, the aperture beinggenerally of the same size as the size of the intersection region.

In accordance with a preferred embodiment of the present invention atleast one of the plurality of optical elements includes at least onenon-focusing optical element. Preferably, the at least one non-focusingelement includes at least one reflective optical element. Alternatively,at least one of the plurality of optical elements includes at least onefocusing element. Preferably, the at least one focusing element includesat least one of a reflective element, a refractive element, adiffractive element and a cylindrical optical element.

In accordance with another preferred embodiment of the present inventionthe passive infra-red detector also includes a window transparent toinfra-red radiation, located adjacent the aperture. Preferably, a centerof the window is located generally at a center of the aperture.

In accordance with yet another preferred embodiment of the presentinvention the window has a circular cross-section. Alternatively, thewindow is generally flat. Preferably, the window is formed of at leastone of HDPE, Silicon and Germanium. Additionally or alternatively, thepassive infra-red detector also includes masking detection functionalityfor providing an alarm output upon detection of masking materialsobstructing the window.

In accordance with still another preferred embodiment of the presentinvention each of the multiple detection zones includes a non-maskedportion when masking materials are applied to part of the window.Preferably, the passive infra-red detector also includes a guard elementsurrounding the window for providing mechanical protection to thewindow. Additionally or alternatively, the passive infra-red detectoralso includes at least one intermediate reflecting surface located alongan optical path defined by the infra-red radiation director at alocation suitable for redirecting radiation from the infra-red radiationdirector to the radiation sensor.

There is further provided in accordance with yet another preferredembodiment of the present invention a radiation detector including ahousing defining an elongate radiation receiving slit aperture lyingalong a slit axis, a radiation sensor disposed within the housing alongthe slit axis at a location spaced from the elongate radiation receivingslit aperture and a radiation reflecting surface arranged to receiveradiation passing through the elongate radiation receiving slit apertureand to focus the radiation on the radiation sensor, the radiationreflecting surface being defined at least partially by rotation througha rotation angle about the slit axis of a portion of a parabola, whoseaxis of symmetry extends perpendicularly to the slit axis through theradiation sensor.

There is even further provided in accordance with still anotherpreferred embodiment of the present invention a radiation detectorincluding a housing defining an elongate radiation receiving slitaperture lying along a slit axis, a radiation sensor disposed within thehousing at a location spaced from the elongate radiation receiving slitaperture and a radiation reflecting surface arranged to receiveradiation passing through the elongate radiation receiving slit apertureand to focus the radiation on the radiation sensor, the radiationreflecting surface being defined at least partially by rotation througha rotation angle about the slit axis of a portion of a parabola, whoseaxis of symmetry extends perpendicularly to the slit axis.

In accordance with another preferred embodiment of the present inventionthe rotation angle is 90 degrees. Additionally or alternatively, theradiation detector is operative such that when the slit axis is ahorizontal axis, the rotation angle defines the angular extent of aradiation receiving curtain in a vertical plane.

In accordance with still another preferred embodiment of the presentinvention the radiation detector also includes at least one intermediatereflecting surface located along an optical path defined by theradiation reflecting surface at a location suitable for redirectingradiation from the radiation reflecting surface to the radiation sensor.

In accordance with yet another preferred embodiment of the presentinvention the radiation detector also includes a window transparent toinfra-red radiation, located adjacent the radiation receiving slitaperture. Additionally, a center of the window is located generally at acenter of the radiation receiving slit aperture. Preferably, the windowhas a circular cross-section. Alternatively, the window is generallyflat.

In accordance with another preferred embodiment of the present inventionthe window does not have optical power and does have varying thickness,thereby providing varying radiation attenuation. Additionally, thevarying radiation attenuation provides pet immunity.

Preferably, the window is formed of at least one of HDPE, Silicon andGermanium.

In accordance with still another preferred embodiment of the presentinvention the radiation reflecting surface includes a plurality ofreflecting surface areas corresponding to a plurality of radiationreceiving areas, wherein different ones of the plurality of reflectingsurface areas have different widths, thereby providing differentsensitivity of the radiation sensor at corresponding ones of theplurality of radiation receiving areas. Additionally, the differentsensitivity of the radiation sensor at corresponding ones of theplurality of radiation receiving areas provides pet immunity.

In accordance with yet another preferred embodiment of the presentinvention the radiation sensor is operative to view a field-of-viewincluding a curtain-like field-of-view. Preferably, the curtain-likefield-of-view extends generally through 90 degrees. Additionally, thecurtain-like field-of-view extends generally through 90 degrees from thevertical to the horizontal.

There is still further provided in accordance with even a furtherpreferred embodiment of the present invention a radiation detectorincluding a housing defining a radiation receiving slit aperture and anoptical system disposed within the housing defining a field-of-view andincluding at least one radiation reflecting surface arranged to receiveradiation passing through the radiation receiving slit aperture and tofocus the radiation on a radiation sensor disposed in the housing, theat least one radiation reflecting surface being defined by a collectionof curves disposed along an ellipse, the ellipse having a first focusand a second focus along a principal axis thereof, the at least oneradiation reflecting surface defining a slit axis which passes throughthe second focus and the slit aperture, each of the curves being definedby the intersection at a point on the ellipse, of a slit axis planewhich includes the slit axis and a focusing surface whose focus is atthe first focus and which has an axis of symmetry which is parallel tothe slit axis plane.

There is yet further provided in accordance with yet another preferredembodiment of the present invention a radiation detector including ahousing defining a radiation receiving slit aperture and an opticalsystem disposed within the housing defining a field-of-view andincluding at least one radiation reflecting surface arranged to receiveradiation passing through the radiation receiving slit aperture and tofocus the radiation on a radiation sensor disposed in the housing, theat least one radiation reflecting surface being defined by a collectionof curves disposed along at least one ellipse, the at least one ellipselying in the same plane and having a common first focus and a commonsecond focus along a principal common axis thereof, the at least oneradiation reflecting surface defining a slit axis which passes throughthe second focus and the slit aperture, each of the curves being definedby the intersection at a point on the at least one ellipse, of a slitaxis plane which includes the slit axis and a focusing surface whosefocus is at the first common focus and which has an axis of symmetrywhich is parallel to the slit axis plane.

In accordance with another preferred embodiment of the present inventionthe slit axis is generally perpendicular to the principal axis.Additionally or alternatively, the focusing surface includes at leastone of a parabolic focusing surface, a spherical focusing surface and anaspheric focusing surface.

There is also provided in accordance with another preferred embodimentof the present invention a radiation detector including a housingdefining a radiation receiving slit aperture and an optical systemdisposed within the housing defining a field-of-view and including atleast one radiation reflecting surface arranged to receive radiationpassing through the radiation receiving slit aperture and to focus theradiation on a radiation sensor disposed in the housing, the at leastone radiation reflecting surface including at least one radiationreflecting surface segment curved in at least two mutually orthogonalplanes, each of the at least one radiation reflecting surface segmentbeing defined by an array of curves which intersect an ellipse having afirst focus at a first common focus point and a second focus in thevicinity of the slit aperture, each of the array of curves being focusedat the first focus of the ellipse.

In accordance with yet another preferred embodiment of the presentinvention each of the array of curves includes at least one of aparabolic curve, a spherical curve and an aspheric curve.

In accordance with still another preferred embodiment of the presentinvention the radiation sensor is located at the first focus.

In accordance with another preferred embodiment of the present inventionthe radiation detector also includes at least one intermediatereflecting surface located along an optical path defined by the at leastone radiation reflecting surface at a location suitable for redirectingradiation from the at least one radiation reflecting surface to theradiation sensor.

In accordance with yet another preferred embodiment of the presentinvention the field-of-view includes a curtain-like field-of-view.Preferably, the curtain like field-of-view extends generally through 90degrees. Additionally, the curtain like field-of-view extends generallythrough 90 degrees from the vertical to the horizontal.

In accordance with still another preferred embodiment of the presentinvention the radiation detector also includes a window transparent toinfra-red radiation, located adjacent the radiation receiving slitaperture. Additionally, a center of the window is located generally at acenter of the radiation receiving slit aperture. Preferably, the windowhas a circular cross-section. Alternatively, the window is generallyflat.

In accordance with yet another preferred embodiment of the presentinvention the window does not have optical power and does have varyingthickness, thereby providing varying radiation attenuation.Additionally, the varying radiation attenuation provides pet immunity.

In accordance with another preferred embodiment of the present inventionthe window is formed of at least one of HDPE, Silicon and Germanium.

Preferably, the at least one radiation reflecting surface includes aplurality of reflecting surface areas corresponding to a plurality ofradiation receiving areas, wherein different ones of the plurality ofreflecting surface areas have different widths thereby providingdifferent sensitivity of the radiation sensor at corresponding ones ofthe plurality of radiation receiving areas. Additionally, the differentsensitivity of the radiation sensor at corresponding ones of theplurality of radiation receiving areas provides pet immunity.

In accordance with yet another preferred embodiment of the presentinvention the slit aperture has a height in the range of 2-5 mm.

There is further provided in accordance with still another preferredembodiment of the present invention a radiation detector including ahousing defining an elongate radiation receiving slit aperture throughwhich extend a first plurality of slit axes, each of the plurality ofslit axes passing through a common first focus of a second plurality ofellipses having a common second focus, the common first focus and thecommon second focus lying along a common primary axis of symmetry, aradiation sensor disposed within the housing and a radiation reflectingsurface arranged to receive radiation passing through the elongateradiation receiving slit aperture and to focus the radiation on theradiation sensor, the radiation reflecting surface including a firstplurality of radiation reflecting surface segments, each of the firstplurality of radiation reflecting surface segments including a segmentsurface curved in at least two mutually orthogonal planes, each thesegment surface including a portion of at least one of the secondplurality of ellipses and being defined by a continuous array of curveswhich join the portion of the at least one of the second plurality ofellipses, the continuous array of curves being focused at the commonsecond focus of the second plurality of ellipses.

In accordance with another preferred embodiment of the present inventioneach of the array of curves includes at least one of a parabolic curve,a spherical curve and an aspheric curve. In accordance with yet anotherpreferred embodiment of the present invention the radiation sensor islocated at the common second focus of the second plurality of ellipses.

In accordance with still another preferred embodiment of the presentinvention the radiation detector also includes at least one intermediatereflecting surface located along an optical path defined by theradiation reflecting surface at a location suitable for redirectingradiation from the radiation reflecting surface to the radiation sensor.In accordance with yet another preferred embodiment of the presentinvention the first plurality of slit axes are generally perpendicularto the common primary axis of symmetry.

In accordance with yet another preferred embodiment of the presentinvention the radiation reflecting surface defines a plurality ofcurtain-like detection zones. Preferably, each of the plurality ofcurtain like detection zones extends generally through 90 degrees.Additionally, each of the plurality of curtain like detection zonesextends generally through 90 degrees from the vertical to thehorizontal.

In accordance with still another preferred embodiment of the presentinvention the radiation detector also includes a window transparent toinfra-red radiation, located adjacent the radiation receiving slitaperture. Preferably, a center of the window is located generally at acenter of the radiation receiving slit aperture. Additionally, thewindow has a circular cross-section. Alternatively, the window isgenerally flat.

In accordance with yet another preferred embodiment of the presentinvention the window does not have optical power and does have varyingthickness, thereby providing varying radiation attenuation. Preferably,the varying radiation attenuation provides pet immunity.

In accordance with another preferred embodiment of the present inventionthe window is formed of at least one of HDPE, Silicon and Germanium.

In accordance with yet another preferred embodiment of the presentinvention the radiation reflecting surface includes a plurality ofreflecting surface areas corresponding to a plurality of radiationreceiving areas, wherein different ones of the plurality of reflectingsurface areas have different widths thereby providing differentsensitivity of the radiation sensor at corresponding ones of theplurality of radiation receiving areas. Preferably, the differentsensitivity of the radiation sensor at corresponding ones of theplurality of radiation receiving areas provides pet immunity.

In accordance with still another preferred embodiment of the presentinvention the window has a height in the range of 2-5 mm.

There is even further provided in accordance with still anotherpreferred embodiment of the present invention a passive infra-reddetector including at least two sub-detectors each operative to receiveinfra-red radiation from a corresponding one of at least two subfields-of-view and signal processing circuitry, receiving output signalsfrom the at least two sub-detectors and noting time relationships of theoutput signals from the at least two sub-detectors and providing amotion detection output in response to receipt of the output signalsfrom the at least two sub-detectors having a time relationship whichmeets at least one predetermined criterion, at least one of the at leastone predetermined criterion being time duration of at least one of theoutput signals.

In accordance with another preferred embodiment of the present inventiontwo of the at least two sub-detectors have substantial horizontalseparation therebetween. Preferably, the at least one predeterminedcriterion is based at least in part on the extent of the substantialhorizontal separation.

In accordance with yet another preferred embodiment of the presentinvention the at least two sub-detectors are angled with respect to eachother by a horizontal separation angle and the at least onepredetermined criterion is based at least in part on the extent of thehorizontal separation angle. In accordance with still another preferredembodiment of the present invention each of the at least two subfields-of-view includes at least one detection zone which diverges by acorresponding horizontal divergence angle and the at least onepredetermined criterion is based at least in part on the extent of thehorizontal divergence angles.

In accordance with another preferred embodiment of the present inventionthe at least one predetermined criterion includes at least one ofwhether a time duration of at least one of the output signals lieswithin a predetermined range of values, whether a time duration betweenreceipt of a first output signal from a first one of the at least twosub-detectors and receipt of a second output signal from a second one ofthe at least two sub-detectors lies within a predetermined range ofvalues, whether a ratio of a first time duration of the first outputsignal and a second time duration of the second output signal lieswithin a predetermined range of values, whether a ratio of the firsttime duration of the first output signal and the time duration betweenreceipt of a first output signal from a first one of the at least twosub-detectors and receipt of a second output signal from a second one ofthe at least two sub-detectors lies within a predetermined range ofvalues and whether a ratio of the second time duration of the secondoutput signal and the time duration between receipt of a first outputsignal from a first one of the at least two sub-detectors and receipt ofa second output signal from a second one of the at least twosub-detectors lies within a predetermined range of values.

In accordance with yet another preferred embodiment of the presentinvention the signal processing circuitry utilizes the timerelationships of the output signals from the at least two sub-detectorsto compute a speed of motion of an intruder generating the outputsignals and provides the motion detection output if the speed of motionis within a predetermined speed range. Preferably, the predeterminedspeed range is between 0.1 to 3 meters per second.

Additionally or alternatively, the signal processing circuitry utilizesthe time relationships of the output signals from the at least twosub-detectors to compute a distance from the detector of an intrudergenerating the output signals and provides the motion detection outputif the distance is within a predetermined distance range. Alternativelyor additionally, the signal processing circuitry utilizes the extent ofat least one of the substantial horizontal separation between the atleast two sub-detectors; the horizontal separation angle between the atleast two sub fields-of-view and a divergence angle of at least onedetection zone of at least one of the at least two sub fields-of-view tocompute the distance and provides the motion detection output if thedistance is within the predetermined distance range.

Additionally or alternatively, the signal processing circuitry utilizesthe time relationships of the output signals from the at least twosub-detectors to compute a ratio representing an extent of change in aspeed of motion of an intruder generating the output signals of the atleast two sub-detectors and provides the motion detection output if theratio, representing the extent of change in the speed of motion of theintruder, is within a predetermined ratio range. Alternatively oradditionally, the signal processing circuitry utilizes the timerelationships of the output signals from the at least two sub-detectorsto compute a ratio (t₁/t₂)/(Z₀/t/K) representing an extent of change ina speed of motion of an intruder generating the output signals of the atleast two sub-detectors and provides the motion detection output if theratio (t₁/t₂)/(Z₀/t/K) is within a predetermined ratio range.Preferably, predetermined ratio range is within at least one of theranges 0.7 to 1.5 and 0.8 to 1.3.

In accordance with another preferred embodiment of the present inventionat least one of the at least two sub fields-of-view includes acurtain-like sub field-of-view. Preferably, the curtain-like subfield-of-view extends generally through 90 degrees. Additionally, thecurtain-like sub field-of-view extends generally through 90 degrees fromthe vertical to the horizontal.

In accordance with yet another preferred embodiment of the presentinvention at least one of the at least two sub fields-of-view includes anon-curtain like sub field-of-view.

In accordance with another preferred embodiment of the present inventionat least one of the at least two sub-detectors includes a single elementsensor. Alternatively or additionally, at least one of the at least twosub-detectors includes a multiple element sensor.

In accordance with yet another preferred embodiment of the presentinvention the signal processing circuitry also includes a traversallogic functionality, which provides an alarm enabling signal based atleast in part on a direction of traversal of the at least two subfields-of-view, and provides the motion detection output based at leastin part on the alarm enabling signal.

In accordance with another preferred embodiment of the present inventionthe traversal logic functionality provides the alarm enabling signal ifat least one of the at least two sub fields-of-view was traversed.Additionally or alternatively, the traversal logic functionalityprovides the alarm enabling signal if at least two of the at least twosub fields-of-view were traversed. Additionally, the traversal logicfunctionality provides the alarm enabling signal if at least two of theat least two sub fields-of-view were traversed in a first direction andwere not traversed in a second direction, generally opposite to thefirst direction. Alternatively or additionally, the traversal logicfunctionality provides the alarm enabling signal if at least two of theat least two sub fields-of-view were traversed in a first direction atleast a predetermined time following traversal of the at least two subfields-of-view in a second direction, generally opposite to the firstdirection.

There is still further provided in accordance with yet another preferredembodiment of the present invention a passive infra-red detectorincluding at least two sub-detectors, each operative to receiveinfra-red radiation from a corresponding one of at least two subfields-of-view and signal processing circuitry, receiving output signalsfrom the at least two sub-detectors and noting time relationships of theoutput signals from the at least two sub-detectors and providing amotion detection output in response to receipt of the output signalsfrom the at least two sub-detectors, representing traversal of the atleast two sub fields-of-view, having a time relationship which meets atleast one predetermined criterion, at least one of the at least onepredetermined criterion being traversal of the at least two subfields-of-view in a first direction at least a predetermined timefollowing traversal of the at least two sub fields-of-view in a seconddirection, generally opposite to the first direction.

In accordance with another preferred embodiment of the present inventionthe signal processing circuitry selectably provides at least one of avisual indication and an audible indication during the predeterminedtime. Additionally, the signal processing circuitry selectably providesboth the visual indication and the audible indication during thepredetermined time.

In accordance with another preferred embodiment of the present inventionthe predetermined time is defined by a user.

There is yet further provided in accordance with even a furtherpreferred embodiment of the present invention an intrusion detectorincluding a housing and at least first and second passive infra-reddetectors disposed in the housing, each being adapted for providing aseparate detector output to an external alarm controller, each of thefirst and second passive infra-red detectors having a plurality ofdetection zones, the detection zones of the first passive infra-reddetector being non-overlapping with the detection zones of the secondpassive infra-red detector, detection zones of the first passiveinfra-red detector being azimuthally interlaced with detection zones ofthe second passive infra-red detector.

In accordance with another preferred embodiment of the present inventionthe at least first and second passive infra-red detectors are arrangedto provide coverage over generally the same azimuthal detection region.In accordance with yet another preferred embodiment of the presentinvention individual detection zones of the first passive infra-reddetector are each located intermediate a pair of individual detectionzones of the second passive infra-red detector. Additionally oralternatively, individual detection zones of the second passiveinfra-red detector are each located intermediate a pair of individualdetection zones of the first passive infra-red detector.

In accordance with still another preferred embodiment of the presentinvention the detection zones of the first passive infra-red detectorare azimuthally interlaced with detection zones of the second passiveinfra-red detector at least at a central portion of the azimuthaldetection region. Additionally or alternatively, the detection zones ofthe first passive infra-red detector are azimuthally interlaced withdetection zones of the second passive infra-red detector in a patternsuch that interference confined to one detection zone of the firstpassive infra-red detector is not sensed by an adjacent detection zoneof the second passive infra-red detector.

In accordance with another preferred embodiment of the present inventionthe intrusion detector also includes at least first and second signalprocessing circuits associated with each of the at least first andsecond passive infra-red detectors and at least first and second outputrelays associated with the first and second signal processing circuitsand being operative to provide the separate detector outputs to theexternal alarm controller.

In accordance with yet another preferred embodiment of the presentinvention the at least first and second output relays are operative toprovide the separate detector outputs to the external alarm controllervia corresponding at least first and second connection wires.Alternatively, the at least first and second output relays include atleast first and second wireless output transmitters.

In accordance with still another preferred embodiment of the presentinvention one of the at least first and second signal processingcircuits is operative to generate a detection output signal and toprovide the detection output signal to the external alarm controlleronly if another of the at least first and second signal processingcircuits detects motion within a predetermined time separation withrespect to the generation of the detection output signal by the one ofthe at least first and second signal processing circuits. Additionallyor alternatively, one of the at least first and second signal processingcircuits is operative to generate a detection output signal and toprovide the detection output signal to the external alarm controlleronly if another of the at least first and second signal processingcircuits generates a detection output signal within a predetermined timeseparation with respect to the generation of the detection output signalby the one of the at least first and second signal processing circuits.Alternatively or additionally, one of the at least first and secondsignal processing circuits is operative to generate a detection outputsignal and to provide the detector output signal to the external alarmcontroller only if another of the at least first and second signalprocessing circuits does not simultaneously generate a detection outputsignal.

In accordance with another preferred embodiment of the present inventionthe at least first and second signal processing circuits are operativeto provide a common detection output signal to the external alarmcontroller.

In accordance with still another preferred embodiment of the presentinvention each of the plurality of detection zones includes a pluralityof finger-like regions. Additionally, the plurality of finger-likeregions includes four finger-like regions.

In accordance with another preferred embodiment of the present inventioneach of the plurality of detection zones includes a pair of verticallyseparated detection zones. Additionally, at least one of the pair ofvertically separated detection zones includes a curtain-like detectionzone.

In accordance with still another preferred embodiment of the presentinvention each of the plurality of detection zones includes a singlevertically distributed curtain-like detection zone.

In accordance with another preferred embodiment of the present inventionthe plurality of detection zones is defined by a corresponding pluralityof optical elements. Additionally, at least one of the correspondingplurality of optical elements includes at least one non-focusing opticalelement. Additionally, the at least one non-focusing optical elementincludes at least one reflective optical element.

Alternatively, at least one of the corresponding plurality of opticalelements includes at least one focusing element. Additionally, the atleast one focusing element includes at least one of a reflectiveelement, a refractive element, a diffractive element and a cylindricaloptical element.

There is still further provided in accordance with yet another preferredembodiment of the present invention a passive infra-red detector havinga field-of-view including multiple detection zones, the detectorincluding a housing adapted for mounting adjacent a ceiling of a roomand having at least one aperture for passage of infra-red radiationtherethrough, at least one sensor disposed in the housing and at leastone infra-red radiation director including a plurality of infra-redoptical elements associated with corresponding ones of the multipledetection zones, each of the plurality of infra-red optical elementsbeing operative to receive infra-red radiation from at least one of themultiple detection zones and to direct the infra-red radiation to the atleast one sensor along a corresponding radiation path, a plurality ofthe radiation paths generally intersecting at an intersection regionlocated at the at least one aperture, the at least one aperture beinggenerally of the same size as the size of the intersection region.

There is yet further provided in accordance with still another preferredembodiment of the present invention a passive infra-red detector havinga field-of-view including multiple detection zones, the detectorincluding a housing adapted for mounting adjacent a ceiling of a roomand having at least one aperture for passage of infra-red radiationtherethrough, at least one sensor disposed in the housing and at leastone infra-red radiation director including multiple infra-red opticalelements, each of the multiple detection zones being exclusively definedby one of the multiple infra-red optical elements which does not defineany other of the multiple detection zones; the multiple infra-redoptical elements being operative to receive infra-red radiation from themultiple detection zones and to direct the infra-red radiation to the atleast one sensor along a corresponding radiation path, a plurality ofthe radiation paths generally intersecting at an intersection regionlocated at the at least one aperture, the at least one aperture beinggenerally of the same size as the intersection region.

In accordance with another preferred embodiment of the present inventionthe housing includes a first housing surface adapted to lie generallyparallel to the ceiling and the at least one aperture is formed in asecond housing surface extending generally parallel to the first housingsurface. In accordance with yet another preferred embodiment of thepresent invention the at least one aperture includes a plurality ofapertures and the at least one sensor includes a single sensor.

In accordance with still another preferred embodiment of the presentinvention the at least one aperture includes a first plurality ofapertures and wherein the at least one sensor includes a number ofsensors which is less than the first plurality. Alternatively, the atleast one aperture includes a first plurality of apertures, the at leastone sensor includes a first plurality of sensors and infra-red radiationreceived by each of the first plurality of sensors is directed through adifferent one of the first plurality of apertures. Alternatively, the atleast one aperture includes a single aperture and wherein the at leastone sensor includes a single sensor.

In accordance with another preferred embodiment of the present inventionthe housing is adapted for mounting adjacent the ceiling in a corner ofthe room.

In accordance with still another preferred embodiment of the presentinvention at least one of the plurality of infra-red optical elementsincludes a non focusing optical element. Additionally, the non-focusingelement is a reflective optical element. Additionally or alternatively,at least one of the plurality of infra-red optical elements includes afocusing element. Additionally, the focusing element includes at leastone of a reflective element, a refractive element, a diffractive elementand a cylindrical optical element.

In accordance with another preferred embodiment of the present inventionthe passive infra-red detector also includes a window transparent toinfra-red radiation, located adjacent the at least one aperture. Inaccordance with yet another preferred embodiment of the presentinvention a center of the window is located generally at a center of theat least one aperture.

In accordance with still another preferred embodiment of the presentinvention the window has a circular cross-section. Alternatively, thewindow is generally flat. Preferably, the window is formed of at leastone of HDPE, Silicon and Germanium.

In accordance with another preferred embodiment of the present inventionthe passive infra-red detector also includes masking detectionfunctionality for providing an alarm output upon detection of maskingmaterials obstructing the window. In accordance with yet anotherpreferred embodiment of the present invention the passive infra-reddetector also includes a guard element surrounding the window forproviding mechanical protection to the window.

In accordance with still another preferred embodiment of the presentinvention the passive infra-red detector also includes at least oneintermediate reflecting surface located along an optical path defined bythe at least one infra-red radiation director at a location suitable forredirecting radiation from the at least one infra-red radiation directorto the at least one sensor. In accordance with another preferredembodiment of the present invention the at least one intermediatereflecting surface includes a single hyperbolic reflecting surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a simplified pictorial illustration of a detector, includinglenses, constructed and operative in accordance with a preferredembodiment of the present invention;

FIG. 2 is a simplified sectional illustration of the detector of FIG. 1,taken along section lines II-II in FIG. 1;

FIG. 3 is a simplified illustration of part of the detector of FIGS. 1and 2, showing details of detection zones;

FIG. 4 is a simplified pictorial illustration of a detector, includingmirrors instead of lenses, constructed and operative in accordance withanother preferred embodiment of the present invention;

FIG. 5 is a simplified sectional illustration of the detector of FIG. 4,taken along section lines V-V in FIG. 4;

FIG. 6 is a simplified illustration of the detector of FIGS. 4 and 5,showing details of detection zones;

FIG. 7A is a simplified illustration of intruder responsive outputs ofdual element sensors, of two adjacent respective sub-detectors in theembodiments of FIGS. 1-6, whose fields-of-view do not overlap;

FIG. 7B is a simplified illustration of intruder responsive outputs ofdual element sensors, of two adjacent respective sub-detectors in theembodiments of FIGS. 1-6, whose fields-of-view do overlap;

FIG. 8A is a simplified illustration of a signal indicative of a typicalhuman intrusion sensed by a detector of the type shown in FIGS. 1-3which has sub-detectors whose fields-of-view do not overlap;

FIGS. 8B-8G are each a simplified illustration of a different signalwhich is not typical of a human intrusion sensed by a detector of thetype shown in FIGS. 1-3 which has sub-detectors whose fields-of-view donot overlap;

FIG. 9A is a simplified illustration of a signal indicative of a typicalhuman intrusion sensed by a detector of the type shown in FIGS. 4-6which has sub-detectors whose fields-of-view overlap;

FIGS. 9B-9G are each a simplified illustration of a different signalwhich is not typical of a human intrusion sensed by a detector of thetype shown in FIGS. 4-6 which has sub-detectors whose fields-of-viewoverlap;

FIG. 10 is a simplified pictorial illustration of a detector, includinglenses, constructed and operative in accordance with yet anotherpreferred embodiment of the present invention;

FIG. 11 is a simplified sectional illustration of a detector employinglenses constructed and operative in accordance with still anotherpreferred embodiment of the present invention;

FIG. 12 is a simplified pictorial illustration of a detector constructedand operative in accordance with a further preferred embodiment of thepresent invention;

FIG. 13 is a simplified sectional illustration of the detector of FIG.12, taken along section lines XIII-XIII in FIG. 12;

FIG. 14 is a simplified pictorial illustration of a detector constructedand operative in accordance with a yet further preferred embodiment ofthe present invention, employing mirrors instead of lenses;

FIG. 15 is a simplified sectional illustration taken along the linesXV-XV in FIG. 14;

FIG. 16 is a simplified illustration of a detector constructed andoperative in accordance with a still further preferred embodiment of thepresent invention;

FIG. 17 is a simplified illustration of a detector constructed andoperative in accordance with an additional preferred embodiment of thepresent invention;

FIG. 18 is a simplified illustration of processing of a signalindicative of a typical human intrusion sensed by a detector of the typeof the detectors of FIGS. 16 and 17;

FIG. 19 is a simplified illustration of processing of a signalindicative of a typical human intrusion sensed by a detector of the typeof the detectors of FIGS. 16 and 17 implementing single element sensors;

FIG. 20 is a simplified flow chart illustrating a preferred embodimentof directional logic particularly useful in the embodiments of FIGS.16-19;

FIG. 21 is a simplified illustration of a detector constructed andoperative in accordance with a further preferred embodiment of thepresent invention;

FIG. 22 is a simplified illustration of a detector constructed andoperative in accordance with another further preferred embodiment of thepresent invention;

FIG. 23 is a simplified illustration of a detector constructed andoperative in accordance with another yet further preferred embodiment ofthe present invention;

FIG. 24 is a simplified illustration of a detector constructed andoperative in accordance with another still further preferred embodimentof the present invention;

FIG. 25 is a simplified illustration of a detector constructed andoperative in accordance with a yet additional preferred embodiment ofthe present invention;

FIG. 26 is a simplified illustration of a detector constructed andoperative in accordance with a still additional preferred embodiment ofthe present invention;

FIG. 27 is a simplified pictorial illustration of a detector constructedand operative in accordance with a further preferred embodiment of thepresent invention;

FIG. 28 is a simplified interior view pictorial illustration of thedetector of FIG. 27;

FIGS. 29A and 29B are simplified sectional illustration taken alongrespective section lines XXIXA-XXIXA and XXIXB-XXIXB in FIG. 28;

FIG. 30 is a simplified pictorial illustration of a detector constructedand operative in accordance with another preferred embodiment of thepresent invention;

FIG. 31 is a simplified interior view pictorial illustration of thedetector of FIG. 29;

FIGS. 32A and 32B are simplified sectional illustration taken alongrespective section lines XXXIIA-XXXIIA and XXXIIB-XXXIIB in FIG. 31;

FIG. 33 is a simplified sectional illustration of a detector constructedand operative in accordance with a still further preferred embodiment ofthe present invention;

FIG. 34 is a simplified pictorial illustration of a detector assemblyconstructed in accordance with yet another preferred embodiment of thepresent invention;

FIGS. 35A and 35B are respective sectional illustrations of the detectorassembly of FIG. 34, taken along respective section lines XXXVA-XXXVAand XXXVB-XXXVB in FIG. 34;

FIGS. 36A and 36B are respectively, a top view illustration and a sideview illustration of a radiation pattern received by the detectorassembly of FIG. 34;

FIG. 37 is a simplified block diagram of the detector assembly of FIG.34;

FIG. 38 is a simplified pictorial illustration of a detector assemblyconstructed in accordance with still another preferred embodiment of thepresent invention;

FIGS. 39A and 39B are respectively, a top view illustration and a sideview illustration of a radiation pattern received by the detectorassembly of FIG. 38;

FIG. 40 is a simplified block diagram of the detector assembly of FIG.38;

FIG. 41 is a simplified pictorial illustration of a detector assemblyconstructed in accordance with a still further preferred embodiment ofthe present invention;

FIGS. 42A and 42B are respectively, a top view illustration and a sideview illustration of a radiation pattern received by the detectorassembly of FIG. 41;

FIG. 43 is a simplified block diagram of the detector assembly of FIG.41;

FIG. 44 is a simplified pictorial illustration of a detector assemblyconstructed in accordance with still another preferred embodiment of thepresent invention;

FIGS. 45A and 45B are respective sectional illustrations of the detectorassembly of FIG. 44, taken along respective section lines XLVA-XLVA andXLVB-XLVB in FIG. 44;

FIGS. 46A and 46B are respectively, a top view illustration and a sideview illustration of a radiation pattern received by the detectorassembly of FIG. 44; and

FIG. 47 is a simplified block diagram of the detector assembly of FIG.44.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For the sake of clarity of description throughout, the followingdefinitions are employed generally throughout.

A “zone” is defined to include fingers of radiation, each correspondingto a detection region seen by a single element of a sensor through anoptical segment, and the region or regions therebetween. Thus, when dualelement sensors are employed, each zone includes two fingers.

A “sub field-of-view” is defined to include one or more zones and theregion or regions therebetween.

A “field-of-view” is defined to include one or more sub fields-of-view.

It is important to note that in detectors designed to protect wideazimuthal areas, the field-of-view may be divided into multiple subfields-of-view, which typically correspond in number to the number oflens or mirror segments in the uppermost row of optical elements.

The term “azimuth” refers to the angular extent of a zone, subfield-of-view or field-of-view in a plane wherein expected intrudermotion mainly takes place. For the purpose of description herein, theterm “horizontal” generally refers to a plane which extends generallyazimuthally. It is assumed that a detector is installed such that itsazimuth is generally parallel to a surface along which motion of theintruder is expected to occur.

When a person moves within the field-of-view of the detector, hetraverses individual zones. As a result, a sensor which is common to allzones produces a series of electrical “desired signals” wherein each“desired signal” at any specific moment in time corresponds to the IRenergy received only from the specific zone viewing the location of theperson at that specific moment. Each sub field-of-view can includevarious zones which may correspond to optical elements located indifferent rows, viewing different parts of the person's bodyconcurrently.

In general, the sensitivity of conventional detectors is selected todetect the level of a “desirable signal” that is received from a singlezone or sub field-of-view when a person passes therethrough.

In accordance with a preferred embodiment of the present invention, thefield-of-view is divided into generally non-overlapping subfields-of-view, each associated with a separate sensor. Each such sensorreceives radiation only from the sub field-of-view with which it isassociated and not from the other sub fields-of-view. As explainedhereinabove, each such sub field-of-view is associated with certainsegments of the detector's lens or mirror assembly, and not with theentire optical system. In a preferred design, the multiple sensors andtheir associated optical segments are optically separated from eachother, for instance by partitions, compartments or by the opticaldesign, so that each sensor does not view the sub fields-of-viewassociated with other sensors.

Accordingly, the present invention provides an improved detector, whichcomprises a multiplicity of sub-detectors, each sub-detector comprisinga sensor and one or more optical segments defining its corresponding subfield-of-view. Therefore, each sub-detector views only a part of theentire area covered by the detector. As a result, at any given time,each sensor is exposed to “desired signals”, and interference, comingonly from one sub field-of-view and only from the optical element oroptical elements associated with that sub field-of-view.

Reference is now made to FIGS. 1-3, which illustrate a lens-basedoutdoor detector constructed and operative in accordance with apreferred embodiment of the present invention. Specifically, FIG. 1 is ageneral view of a detector comprising seven sub-detectors, eachsub-detector including a pyroelectric sensor associated with one or morecorresponding lens segments, defining a corresponding sub field-of-view.The seven sub fields-of-view are preferably, but not necessarily, notoverlapping. As shown in FIG. 2, each of the seven sub fields-of-viewincludes two mutually vertically separated zones.

Preferably, the sub fields-of-view, corresponding to each of thesub-detectors, are substantially non-overlapping and are angled withrespect to each other, such that adjacent sub fields-of-view areseparated by no more than 30 degrees or by no more than 3 meters at theeffective far end of the corresponding sub fields-of-view, which isdetermined by the detector design. Such separation between adjacent subfields-of-view provides detection coverage of the field-of-view asrequired by various international standards, such as European standardTS 50131-2-2 and IEC-639-2-6, which require the detector to detect anintruder traversing a distance of three meters at certain angles anddirections. Each of the sub-detectors preferably views a portion of theentire field-of-view of the detector, such that the detector provides awide coverage area, for example having a field-of-view divergence angleof 60 degrees or more.

As seen in FIGS. 1 and 2, the sensors are arranged so that each sensoris exclusively associated with certain lens segments. In the illustratedembodiment, a sensor 10 is associated with lens segments 12 and 14,defining a sub-detector 16. In a similar manner, sensors 20, 30, 40, 50,60 and 70 are associated respectively with lens segments 22 and 24, 32and 34, 42 and 44, 52 and 54, 62 and 64 and 72 and 74, definingrespective sub-detectors 26, 36, 46, 56, 66, and 76. As shown in FIGS. 1and 2, sub-detectors 16, 26, 36, 46, 56, 66 and 76 are preferablyarranged in a convex arrangement in a circular arc within a housingelement 80, thereby together to define the detector, which is designatedby reference numeral 82. Additionally, the detector may also includeseveral sub-detectors associated with one or more common lens segments.

The lens segments 12, 22, 32, 42, 52, 62 and 72 are preferably Fresnellenses, while the lens segments 14, 24, 34, 44, 54, 64 and 74 arepreferably cylindrical type lenses. Any other suitable type of lenselements, such as, for example, diffractive lenses, and any suitablearrangement thereof, may be employed.

Alternatively, each sub-detector may include only a single lens segment.This may be beneficial, for example, if the vertical angle between thesub fields-of-view of lens segments in upper and lower rows of lenssegments is relatively large, so that a person moving in front of thedetector is not normally viewed by both lens segments simultaneously.Such an embodiment reduces the “undesired signals” viewed by eachsub-detector at the expense of increasing the number of sub-detectors.

As a further alternative, each sub-detector may be associated withseveral lens segments, including lens segments lying in the samevertical plane as well as lens segments lying in the same horizontalrow. In such a case, each sub field-of-view includes plural mutuallyazimuthally separated detection zones and plural mutually verticallyseparated detection zones. For instance, a single sub-detector could beassociated with lens segments 22, 32, 24 and 34. This embodiment may bebeneficial for instance in cases where the number or density of the lenssegments within a horizontal row is relatively high and the horizontalangle between the sub fields-of-view of the lens segments is relativelysmall. In such cases it may be possible to reduce the cost of thedetector by reducing the number of the sub-detectors, especially whenthe detector is designed for indoor environments having a moderate levelof “undesired signals”.

As seen in FIGS. 1 and 2, each of sensors 10, 20, 30, 40, 50, 60 and 70of respective sub-detectors 16, 26, 36, 46, 56, 66 and 76 is preferablylocated within a corresponding sub-detector compartment. Thesub-detector compartments are designated respectively by referencenumerals 15, 25, 35, 45, 55, 65 and 75. Each sub-detector compartment isdefined by walls, such as walls 78 of compartment 75, seen clearly inthe enlarged portion of FIG. 1, preferably having wall surfaces whichare generally non-reflective to both IR and visible light. Suitablewalls may be made of black plastic which is preferably conditioned tominimize reflection thereby. This arrangement allows each sensor toreceive only radiation emanating from its corresponding subfield-of-view, as defined by the lens segments associated therewith.

Preferably, each sub-detector compartment is a sealed compartment thatprevents entry of air drafts and insects.

It is a particular feature of an embodiment of the present inventionthat signal processing circuitry which receives output signals from atleast two of sub-detectors 16, 26, 36, 46, 56, 66 and 76, notes multipledetections by one of the sub-detectors within a predetermined first timeperiod and the absence of detections by another of the sub-detectors andis operative to ignore future detections by the sub-detector that hadmultiple detections for at least a predetermined second time period.

Preferably, the signal processing circuitry may ignore the futuredetections only in a case where the initial multiple detections fulfillpredetermined pre-alarm criteria, and are likely to lead to a falsealarm. Additionally or alternatively, the signal processing circuitrymay ignore the future detections only in a case where the multipledetections fulfill predetermined alarm criteria.

The signal processing circuitry may extend the time duration duringwhich the future detections are ignored in response to additionaldetections by the sub-detector during the predetermined second timeperiod.

Additionally or alternatively, the signal processing circuitry may notea sequence of receipt of the output signals from sub-detectors 16, 26,36, 46, 56, 66 and 76 and may provide motion path output informationbased on this sequence.

In accordance with a preferred embodiment of the present invention andas seen with particularity in FIG. 3, sensors 10, 20, 30, 40, 50, 60 and70 each comprise dual element pyroelectric sensors, such as Perkin-ElmerLHi-968 sensors, each having first and second sensing elements 84 and86, separated by a distance D.

FIG. 3 shows the detection fingers of each of sensing elements 84 and 86for two adjacent sub-detectors such as sub-detectors 66 and 76 ofdetector 82. In the illustrated embodiment of FIG. 3, each sub-detectorhas a sub field-of-view, respectively indicated by reference numerals 87and 88, each sub field-of-view having a central axis designated byreference numeral 89. FIGS. 2 and 3 show adjacent sub fields-of-view 87and 88, defined by adjacent lens segments, respectively designated byreference numerals 92 and 93. The detection fingers in each of subfields-of-view 87 and 88 are designated by reference numerals 94 and 96in FIG. 3.

As seen in FIG. 3, each of the fingers 94 and 96 of each of the subfields-of-view 87 and 88 is centered on a central axis indicated byreference numeral 98.

Several different angles may be seen in FIG. 3. Angle A separates thecentral axes 89 of adjacent sub fields-of-view 87 and 88. Angle Bseparates each of the central axes 98 of the fingers and the adjacentcentral axis 89 for each corresponding sub field-of-view. Accordingly,the angle between central axes 98 of adjacent fingers 94 and 96 in eachsub field-of-view is 2B. Each of the fingers 94 and 96 diverges by adivergence angle C.

Reference is now made to FIGS. 4-6, which illustrate a detectorconstructed and operative in accordance with another preferredembodiment of the invention. The detector of FIGS. 4-6 is similar tothat of FIGS. 1-3, with the lens segments in FIGS. 1-3 being replaced bymirror segments.

FIGS. 4, 5 and 6 illustrate a mirror-based outdoor detector constructedand operative in accordance with a preferred embodiment of the presentinvention. FIG. 4 is a general view of a detector comprising sevensub-detectors, each sub-detector including a pyroelectric sensorassociated with one or more corresponding mirror elements, defining acorresponding sub field-of-view. The seven sub fields-of-view arepreferably, but not necessarily, not overlapping.

Preferably, the sub fields-of-view, corresponding to each of thesub-detectors, are substantially non-overlapping and are angled withrespect to each other, such that adjacent sub fields-of-view areseparated by no more than 30 degrees or by no more than 3 meters at theeffective far end of the corresponding sub fields-of-view, which isdetermined by the detector design. Such separation between adjacent subfields-of-view provides detection coverage of the field-of-view asrequired by various international standards, such as European standardTS 50131-2-2 and IEC-639-2-6, which require the detector to detect anintruder traversing a distance of three meters at certain angles anddirections. Each of the sub-detectors preferably views a portion of theentire field-of-view of the detector, such that the detector provides awide coverage area, for example, having a field-of-view divergence angleof 60 degrees or more.

As seen in FIGS. 4 and 5, the sensors are arranged so that each sensoris exclusively associated with a single mirror segment. As seenparticularly in FIG. 5, a sensor 110 is associated with a mirror segment112, defining a sub-detector 116. In a similar manner, sensors 120, 130,140, 150, 160 and 170 are associated with respective mirror segments122, 132, 142, 152, 162 and 172, defining respective sub-detectors 126,136, 146, 156, 166 and 176. As shown in FIGS. 4 and 5, sub-detectors116, 126, 136, 146, 156, 166 and 176 are preferably arranged in a convexarrangement in a circular arc within a housing element 180, therebytogether to define the detector, which is designated by referencenumeral 182. Alternatively, the detector may include severalsub-detectors associated with one or more common mirror segments.

As seen in FIGS. 4 and 5, each of sensors 110, 120, 130, 140, 150, 160and 170 of respective sub-detectors 116, 126, 136, 146, 156, 166 and 176is preferably located within a corresponding sub-detector compartment.The sub-detector compartments are designated respectively by referencenumerals 115, 125, 135, 145, 155, 165 and 175. Each sub-detectorcompartment is defined by walls, such as walls 178 of compartment 175seen clearly in the enlarged portion of FIG. 4, preferably having wallsurfaces which are generally non-reflective to both IR and visiblelight. Suitable walls may be made of black plastic which is preferablyconditioned to minimize reflection thereby. This arrangement allows eachsensor to receive only radiation emanating from its corresponding subfield-of-view, as defined by the mirror segment associated therewith.

Alternatively, each sub-detector may be associated with several mirrorsegments, including multiple mirror segments lying in the same verticalplane and/or multiple mirror segments lying in the same horizontal row.In such a case, each sub field-of-view includes plural mutuallyazimuthally separated detection zones and plural mutually verticallyseparated detection zones. For instance, a single sub-detector may beassociated with mirror segments 122 and 132. This embodiment may bebeneficial for instance in cases where the number or density of themirror segments within a horizontal row is relatively high and thehorizontal angle between the zones defined by the mirror segments isrelatively small. In such cases it may be possible to reduce the cost ofthe detector by reducing the number of the sub-detectors, especiallywhen the detector is designed for indoor environments having a moderatelevel of undesired signals.

Preferably, each sub-detector compartment is a sealed compartment thatprevents entry of air drafts and insects. At the front of eachsub-detector compartment there is provided a window, preferably made ofIR transparent material such as thin HDPE. The rear of each sub-detectorcompartment 115, 125, 135, 145, 155, 165 and 175 includes a curvedmirror element, which defines one of mirror segments 112, 122, 132, 142,152, 162 and 172 respectively.

It is a particular feature of an embodiment of the present inventionthat signal processing circuitry which receives output signals from atleast two of sub-detectors 116, 126, 136, 146, 156, 166 and 176, notesmultiple detections by one of the sub-detectors within a predeterminedfirst time period and the absence of detections by another of thesub-detectors and is operative to ignore future detections by thesub-detector that had multiple detections for at least a predeterminedsecond time period.

Preferably, the signal processing circuitry may ignore the futuredetections only in a case where the initial multiple detections fulfillpredetermined pre-alarm criteria, and are likely to lead to a falsealarm. Additionally or alternatively, the signal processing circuitrymay ignore the future detections only in a case where the multipledetections fulfill predetermined alarm criteria.

The signal processing circuitry may extend the time duration duringwhich the future detections are ignored in response to additionaldetections by the sub-detector during the predetermined second timeperiod.

Additionally or alternatively, the signal processing circuitry may notea sequence of receipt of the output signals from sub-detectors 116, 126,136, 146, 156, 166 and 176 and may provide motion path outputinformation based on this sequence.

In accordance with a preferred embodiment of the present invention andas seen with particularity in FIG. 6, sensors 110, 120, 130, 140, 150,160 and 170 each comprise dual element pyroelectric sensors such asPerkin-Elmer LHi-968 sensors, each having first and second sensingelements 184 and 186, separated by a distance D.

FIG. 6 shows the detection fingers of each of sensing elements 184 and186 for two adjacent sub-detectors such as sub-detectors 166 and 176 ofdetector 182. In the illustrated embodiment of FIG. 6, each sub-detectorhas a sub field-of-view, respectively indicated by reference numerals187 and 188, each sub field-of-view having a central axis designated byreference numeral 189. FIGS. 5 and 6 show adjacent sub fields-of-view187 and 188, defined by adjacent mirror segments, respectivelydesignated by reference numerals 192 and 193. The detection fingers ineach of sub fields-of-view 187 and 188 are designated by referencenumerals 194 and 196 in FIG. 6.

As seen in FIG. 6, each of the fingers 194 and 196 of each of the subfields-of-view 187 and 188 is centered on a central axis indicated byreference numeral 198.

Several different angles may be seen in FIG. 6. Angle A separates thecentral axes 189 of adjacent sub fields-of-view 187 and 188. Angle Bseparates each of the central axes 198 of the fingers and the adjacentcentral axis 189 for each corresponding sub field-of-view. Accordingly,the angle between central axes 198 of adjacent fingers 194 and 196 ineach sub field-of-view is 2B. Each of the fingers 194 and 196 divergesby a divergence angle C.

Considering FIGS. 3 and 6 it is appreciated that the sub fields-of-viewof adjacent sub-detectors, such as sub-detectors 66 and 76 in FIG. 3 andsub-detectors 166 and 176 in FIG. 6, are not overlapping if thefollowing angular relationship exists:2B+C<A

As noted above and as is known in the art, the angle B is a function ofthe distance D between adjacent sensing elements, such as sensingelements 84 and 86 in FIG. 3 or sensing elements 184 and 186 in FIG. 6,and/or a function of the focal length of the corresponding opticalelement, such as lens segments 62 or 72 in FIGS. 1 and 2 and mirrorsegments 162 or 172 in FIGS. 4 and 5.

As is known in the art, the angle C is a function of the width of eachsensing element, such as sensing elements 84 and 86 in FIG. 3 or sensingelements 184 and 186 in FIG. 6, and/or a function of the focal length ofthe corresponding optical element, such as lens segments 62 or 72 inFIGS. 1 and 2 and mirror segments 162 or 172 in FIGS. 4 and 5.

As is known in the art, the angle A is a design parameter, which isdetermined based on performance requirements.

It is a particular feature of the present invention that the subfields-of-view of each of the sub-detectors are not entirelyoverlapping. Most preferably, sub fields-of-view of differentsub-detectors do not overlap at all.

Reference is made to FIG. 7A, which illustrates intruder responsiveoutputs of dual element sensors of two adjacent respectivesub-detectors, such as sub-detectors 66 and 76 of the embodiment ofFIGS. 1-3, whose sub fields-of-view do not overlap. It is seen that thesignals do not overlap in time.

FIG. 7B illustrates intruder responsive outputs of dual element sensorsof two adjacent respective sub-detectors, such as sub detectors 66 and76 of the embodiment of FIGS. 1-3, whose sub fields-of-view partiallyoverlap. It is seen that the signals partially overlap in time, buttheir peaks occur at different times.

It is a particular feature of the present invention that the structuredescribed hereinabove with reference to FIGS. 1-6 enables enhancedsignal processing which analyses and distinguishes more clearly betweensignals produced by movement of a person across the field-of-view of thedetector and signals resulting from various types of interference.

For example, it may be assumed that motion of a person past the detectorwill be detected sequentially by at least two adjacent sub-detectorswithin a certain time duration corresponding to the speed of motion ofthe person. Should the signal produced by several sub-detectors not fitinto a predefined pattern, which may be defined by an algorithm, it maybe considered to be a false signal. For example, should the signal bereceived by only one sub-detector, or by two sub-detectors, which arenot adjacent to one another, or should the signal have timing which isnot in conformance with the expected speed of motion of a person, thesignal may be regarded as a false signal and ignored.

Similarly, signals output by several sub-detectors at approximately thesame time, which cannot result from motion of a person therepast, may beignored. Such signals, especially when they have generally similarcharacteristics, such as amplitude, frequency or shape, are mostprobably a result of interference that affects several sub-detectors ina similar way.

FIGS. 8A-8G illustrate examples of signals produced by a detector of amultiple sub-detector embodiment such as detector 82 of FIGS. 1-3,having non-overlapping sub fields-of-view. Shown in FIGS. 8A-8G areseveral examples of signals produced by sensors 50, 60 and 70 ofdetector 82. In FIGS. 8A-9G, t₁ and t₂ represent time intervals betweendetection of motion from one sensor to an adjacent sensor, and T₁, T₂and T₃ represent the duration of signals received by each sensor.

FIG. 8A shows a typical example of signals produced by a person crossingadjacent sub fields-of-view of the sensors 50, 60 and 70. The motion ofthe person is initially detected by sensor 50 and thereafter, after atime interval t₁, the motion of the person is detected by sensor 60.After an additional time interval t₂, the motion of the person isdetected by sensor 70. As can be seen, the signals of the three sensors50, 60 and 70 are received in succession with generally uniform timing(t₁ generally equals t₂) and each signal has generally the same duration(T₁≈T₂≈T₃), which is characteristic of movement of a person in front ofthe detector at a uniform speed and at approximately the same distancefrom the detector.

Signal durations T₁, T₂ and T₃ may vary as a function of the angle 2B+Cof the sub field-of-view of their corresponding sub-detectors 50, 60 and70, as described hereinabove with reference to FIGS. 3 and 6, and of theangular speed of the moving person. Time intervals t₁ and t₂ are afunction of the angle A between two adjacent sub-detectors 50 and 60 or60 and 70, as illustrated in FIGS. 3 and 6, and the angular speed of themoving person. Because the specific design of the detector determinesangles A, B and C, the respective ratios between the durations T₁, T₂and T₃ and the time intervals t₁ and t₂ follow a characteristic patternspecific to the detector and can therefore be analyzed to determinewhether a signal is due to human motion or interference.

If a person moves through the sub fields-of-view of sub-detectors 50, 60and 70 at a generally constant angular speed (i.e. at a uniform speedand at approximately the same distance from the detector), the ratiosT₁/t₁, T₂/t₁, T₂/t₂ and T₃/t₂ are generally the same.

In some designs it may be preferable to determine the duration, T, bymeasuring the time interval between adjacent positive and negative peaksof the sub-detector output signals and to determine the time interval,t, by measuring the time interval between adjacent positive peaks ornegative peaks of two adjacent sub-detector signals.

The signals may differ in amplitude and shape due to variations in thebackground temperature and/or the type of motion. There may also be somevariation in the time intervals (t), durations (T), or the ratios T/t,due to the person changing his speed of motion or distance from thedetector during movement. However, as long as these variations arewithin certain limits, the signal may still be recognized as motion of aperson.

Signal processing methods useful in the analysis of signals obtainedfrom the detectors of the embodiments of FIGS. 1-6, as shown in FIGS.8A-8G, are described in detail hereinbelow with reference to FIGS. 18and 19.

FIG. 8B shows signals from three different sub-detectors havingdifferent time durations. Although the signals occur in succession, itis unlikely that the speed of motion of a person varies to an extentsufficient to produce the differences in duration T₁, T₂ and T₃ and timeintervals t₁ and t₂ as shown in FIG. 8B. It is also unlikely thatsignals resulting from human movement could create the significantvariation in the ratios T₂/t₁, T₂/t₂, and T₃/t₂. Additionally, it isunlikely that there is no time gap between the signals of sensor 60 andsensor 70 when their respective sub fields-of-view do not overlap as inthis embodiment. Therefore the signals of FIG. 8B can be recognized asresulting from interference and not from motion of a person.

FIG. 8C illustrates a case wherein signals are received from sensors 50and 70 but not from sensor 60 which is located therebetween. This isunlikely to be a result of a motion of a person because such motionwould be expected to produce a signal from sensor 60. It is more likelythat this is a result of moving trees or bushes located in the subfields-of-view of sensors 50 and 70 and not in the sub field-of-view ofsensor 60.

FIG. 8D shows signals having the same durations T₁, T₂ and T₃ producedby three different sub-detectors and having uniform shapes butnon-uniform time separations t₁ and t₂ therebetween. Although thesignals occur in succession, it is unlikely that the speed of motion ofa person varies to an extent sufficient to produce the differences intiming t₁ and t₂ as shown in FIG. 8D. Also it is unlikely that there isoverlap between the signals of sensor 50 and sensor 60 when theirrespective sub fields-of-view do not overlap as in this embodiment.Therefore the signals of FIG. 8D can be recognized as resulting frominterference and not from motion of a person.

FIG. 8E illustrates a case wherein signals are received from sensors 50and 60 with a large time difference t₁ therebetween. This is unlikely tobe a result of a motion of a person because such motion would beexpected to produce signal separated by a time interval which issubstantially shorter than t₁.

FIG. 8F shows three signals occurring at approximately the same time.The fact that the signals from sensors 50, 60 and 70 occursimultaneously and have a similar shape, suggests that these signals aredue to interference that affects all three sensors simultaneously and isnot due to motion of a person.

FIG. 8G shows a case wherein only one sensor, sensor 50, provides asignal. As can be seen the signal is non-uniform over time. No signal isproduced by sensors 60 or 70. This may be the result of interferencesuch as a tree or other object moving in the sub field-of-view of onlyone sub-detector.

It is appreciated that FIGS. 8B-8G are merely illustrations of someexamples of spurious signals which can be readily distinguished fromintrusion signals by the detector of the present invention.

FIGS. 9A-9G illustrate examples of signals produced by a detector of amultiple sub-detector embodiment, such as detector 182 of FIGS. 4-6,having partially overlapping sub fields-of-view. Shown in FIGS. 9A-9Gare several examples of signals produced by sensors 150, 160 and 170 ofdetector 182.

FIG. 9A shows a typical example of signals produced by a person crossingadjacent sub fields-of-view of the sensors. The motion of the person isinitially detected by sensor 150 and thereafter, after a time intervalt₁, the motion of the person is detected by sensor 160. After anadditional time interval t₂ the motion of the person is detected bysensor 170. As can be seen, the signals of the three sensors 150, 160and 170 are received in succession with generally uniform timing (t₁generally equals t₂) and each signal has generally the same duration(T₁≈T₂≈T₃), which is characteristic of movement of a person in front ofthe detector at a uniform speed and at approximately the same distancefrom the detector. The signals partially overlap in time to a generallyuniform extent.

As described hereinabove with respect to FIG. 8A, the ratios T₁/t₁,T₂/t₁, T₂/t₂ and T₃/t₂ are generally the same when a person movesthrough the sub fields-of-view of sub-detectors 150, 160 and 170 at agenerally constant angular speed (i.e. at a uniform speed and atapproximately the same distance from the detector).

The signals may differ in amplitude and shape due to variations in thebackground temperature and/or the type of motion. There may also be somevariation in the time intervals (t), durations (T) or the ratio T/t, dueto the person changing his speed of motion or distance from the detectorduring movement. However, as long as these variations are within certainlimits, the signal can be still recognized as motion of a person.

FIG. 9B shows partially overlapping signals from three differentsub-detectors having non-uniform durations T₁, T₂ and T₃ and non-uniformtime separations t₁ and t₂. Additionally, there is a significantdifference in the ratios T₂/t₁, T₂/t₂ and T₃/t₂. Although the signalsoccur in succession, it is unlikely that the speed of motion of a personvaries to an extent sufficient to produce the differences in timeintervals t₁ and t₂ as shown in FIG. 9B. Therefore the signals of FIG.9B can be recognized as resulting from interference and not from motionof a person.

Signal processing methods useful in the analysis of signals obtainedfrom the detectors of the embodiments of FIGS. 1-6, as shown in FIGS.9A-9G, are described in detail hereinbelow with reference to FIGS. 18and 19.

FIG. 9C illustrates a case wherein signals of differing durations arereceived from sensors 150 and 170 but not from sensor 160 which islocated therebetween. This is unlikely to be a result of a motion of aperson because such motion would be expected to produce a signal fromsensor 160. It is more likely that this is a result of moving trees orbushes located in the sub fields-of-view of sensors 150 and 170 and notin the sub field-of-view of sensor 160.

FIG. 9D shows signals having the same durations T₁, T₂ and T₃ producedby three different sub-detectors and having uniform shapes butnon-uniform time separations t₁ and t₂ therebetween. Although thesignals occur in succession, it is unlikely that the speed of motion ofa person varies to an extent sufficient to produce the differences intiming t₁ and t₂ as shown in FIG. 9D. Also it is unlikely that there isno overlap between the signals of sensor 160 and sensor 170 when theirrespective sub fields-of-view do overlap as in this embodiment.Therefore the signals of FIG. 9D can be recognized as resulting frominterference and not from motion of a person.

FIG. 9E shows signals from two adjacent sub-detectors having no overlap,but rather a time interval therebetween. Although the signals occur insuccession, the lack of overlap indicates that the signals of FIG. 9Ecan be recognized as resulting from interference and not from motion ofa person.

FIG. 9F shows three signals occurring at approximately the same time.The fact that the signals from sensors 150, 160 and 170 occursimultaneously and have a similar shape, suggests that these signals aredue to interference that affects all three sensors simultaneously and isnot due to motion of a person.

FIG. 9G shows a case wherein sensors 150 and 160 provide differentsignals, which are non-uniform over time. This may be the result ofinterference such as a tree or other object moving in the fields-of-viewof only two sub-detectors.

It is appreciated that FIGS. 9B-9G are merely illustrations of someexamples of spurious signals which can be readily distinguished fromintrusion signals by the detector of the present invention.

Reference is now made to FIG. 10, which illustrates a lens-based outdoordetector constructed and operative in accordance with another preferredembodiment of the present invention. The embodiment of FIG. 10 issimilar to that of FIG. 1 except that the detector includes two rows ofsub-detectors rather than one.

FIG. 10 is a general view of a detector comprising fourteensub-detectors, each sub-detector including a pyroelectric sensorassociated with one or more corresponding lens segments, defining acorresponding sub field-of-view. Preferably, but not necessarily, thefourteen sub fields-of-view are not overlapping. As shown in FIG. 10,each of the seven sub fields-of-view includes two mutually verticallyseparated zones.

Preferably, the sub fields-of-view corresponding to each of thesub-detectors are substantially non-overlapping and are angled withrespect to each other, such that adjacent sub fields-of-view areseparated by no more than 30 degrees or by no more than 3 meters at theeffective far end of the corresponding sub fields-of-view, which isdetermined by the detector design. Such separation between adjacent subfields-of-view provides detection coverage of the field-of-view asrequired by various international standards, such as European standardTS 50131-2-2 and IEC-639-2-6, which require the detector to detect anintruder traversing a distance of three meters at certain angles anddirections. Each of the sub-detectors preferably views a portion of theentire field-of-view of the detector, such that the detector provides awide coverage area, for example, having a field-of-view divergence angleof 60 degrees or more.

The sensors in FIG. 10 are arranged so that each sensor is exclusivelyassociated with a corresponding one of lens segments 212, 214, 222, 224,232, 234, 242, 244, 252, 254, 262, 264, 272, and 274. In the illustratedembodiment, a sensor 260 is associated with lens segment 262 defining asub-detector 266, a sensor 261 is associated with lens segment 264,defining a sub-detector 267, a sensor 270 is associated with lenssegment 272 defining a sub-detector 276, and a sensor 271 is associatedwith lens segment 274, defining a sub-detector 277. Similarly,associated with lens segments 212, 214, 222, 224, 232, 234, 242, 244,252 and 254 are corresponding sensors, which are not shown in FIG. 10.

It is appreciated that the fourteen sub-detectors of the embodiment ofFIG. 10 are preferably arranged in upper and lower rows, preferablydisposed in respective circular arcs within a housing element 278,thereby together to define the detector, which is designated byreference numeral 280.

The lens segments 212, 222, 232, 242, 252, 262 and 272, are preferablyFresnel lenses, while the lens segments 214, 224, 234, 244, 254, 264,and 274 are preferably cylindrical type lenses. Any other suitable typeof lens elements, such as, for example, diffractive lenses, and anysuitable arrangement thereof, may be employed.

As seen in the enlarged portion of FIG. 10, each of the pairs ofrespective sub-detectors, such as sub-detectors 276 and 277, ispreferably located within a corresponding sub-detector compartment,designated by reference numeral 282. Preferably, a similar structure isfound in all of the corresponding sub-detectors of FIG. 10. Eachsub-detector compartment is defined by walls, such as walls 284 ofcompartment 282, preferably having wall surfaces which are generallynon-reflective to both IR and visible light. Suitable walls may be madeof black plastic, which is preferably conditioned to minimize reflectionthereby. This arrangement allows each sensor to receive only radiationemanating from its corresponding sub field-of-view, as defined by thelens segment associated therewith.

Preferably, each sub-detector compartment is a sealed compartment thatprevents entry of air drafts and insects.

In accordance with a preferred embodiment of the present invention, thefourteen sensors, including sensors 260, 261, 270 and 271 shown in FIG.10, each comprise dual element pyroelectric sensors, such as LHi-968sensors, which are commercially available from Perkin-Elmer of Freemont,Calif., USA.

Reference is now made to FIG. 11, which is a simplified sectionalillustration of a detector 300 constructed and operative in accordancewith yet another preferred embodiment of the present invention. Theembodiment of FIG. 11 may be identical to that of either of FIGS. 1-3and FIG. 10, wherein each Fresnel lens is replaced by a pair ofhorizontally side-by-side Fresnel lens segments. As shown in FIG. 11,each of the seven sub fields-of-view includes a pair of azimuthallyseparated detection zones.

As shown in FIG. 11, sensors 310, 320, 330, 340, 350, 360 and 370 eachcomprise dual element pyroelectric sensors, such as LHi-968 sensors,which are commercially available from Perkin-Elmer of Freemont, Calif.,USA. Each sensor is located in a corresponding sub-detector compartment.The sub-detector compartments are designated respectively by referencenumerals 315, 325, 335, 345, 355, 365 and 375. Respective sub-detectorcompartments and corresponding sensors comprise sub-detectors which aredesignated by reference numerals 316, 326, 336, 346, 356, 366 and 376.

Each sub-detector compartment is defined by walls, similar to walls 284in FIG. 10, which preferably have wall surfaces which are generallynon-reflective to both IR and visible light. Suitable walls may be madeof black plastic, which is preferably conditioned to minimize reflectionthereby. This arrangement of the sensors within individual sub-detectorcompartments allows each sensor to receive only radiation emanating fromits corresponding sub field-of-view, as defined by the lens segmentsassociated therewith.

At the front of each sub-detector compartment there is located a pair ofhorizontally side-by-side Fresnel lens segments, such as lens segments390 and 392 of compartment 375. The lens segments preferably togetherform an IR transparent window through which radiation enters each of thesub-detectors.

It is appreciated that it is not necessary that all sub-detectors of agiven detector include an identical number of lens segments or the samearrangement of the segments. Accordingly it is possible to have, forinstance, a combination of sub-detectors with four lens segments, asexplained hereinabove, together with sub-detectors comprising only oneor two lens segments placed one above or alongside the other, or anyother combination suitable for a given application.

It is also appreciated that a given detector may incorporate multipleelement pyroelectric sensors, rather than a common dual element sensor.As an example, a four element pyroelectric sensor, commonly referred toas a “quad sensor”, such as REP05B, commercially available from NipponCeramics Co. of Japan, may be employed in place of a dual elementsensor. This may apply in principle to any of the detectors describedherein which employ multiple element sensors.

Reference is now made to FIG. 12, which is a simplified pictorialillustration of a detector constructed and operative in accordance withstill another preferred embodiment of the present invention and to FIG.13, which is a simplified sectional illustration of the detector of FIG.12, taken along section lines XIII-XIII in FIG. 12.

The embodiment of FIGS. 12 and 13 incorporates a particularlyadvantageous spatially limited common slit window configuration. As seenparticularly in FIG. 13, the sub fields-of-view of the varioussub-detectors intersect generally at one location. A relatively narrowslit-type aperture, having a window formed therein, is preferablyprovided surrounding the location at which the sub fields-of-viewintersect. The slit-type aperture limits interference and ismechanically robust.

FIG. 12 is a general view of a detector comprising seven sub-detectors,each sub-detector including a pyroelectric sensor associated with one ormore corresponding lens segments, defining a corresponding subfield-of-view. Preferably, but not necessarily, the seven subfields-of-view are not overlapping.

Preferably, the sub fields-of-view, corresponding to each of thesub-detectors, are substantially non-overlapping and are angled withrespect to each other, such that adjacent sub fields-of-view areseparated by no more than 30 degrees or by no more than 3 meters at theeffective far end of the corresponding sub fields-of-view, which isdetermined by the detector design. Such separation between adjacent subfields-of-view provides detection coverage of the field-of-view asrequired by various international standards, such as European standardTS 50131-2-2 and IEC-639-2-6, which require the detector to detect anintruder traversing a distance of three meters at certain angles anddirections. Each of the sub-detectors preferably views a portion of theentire field-of-view of the detector, such that the detector provides awide coverage area, for example, having a field-of-view divergence angleof 60 degrees or more.

As seen in FIGS. 12 and 13, the sub-detectors are arranged in a mutuallyconcave arrangement, so that each sensor is exclusively associated withcertain lens segments. In the illustrated embodiment, a sensor 410 isassociated with lens segment 415, defining a sub-detector 416. In asimilar manner, sensors 420, 430, 440, 450, 460 and 470 are associatedwith respective lens segments 425, 435, 445, 455, 465 and 475, definingrespective sub-detectors 426, 436, 446, 456, 466 and 476.

As shown in FIGS. 12 and 13, sub-detectors 416, 426, 436, 446, 456, 466and 476 are preferably arranged in a concave arrangement in a circulararc within a housing element 480, thereby together to define thedetector, which is designated by reference numeral 482.

The housing element defines a relatively narrow slit aperture 483adjacent which is preferably located a common window 484, preferablyhaving a circular cross-section with its center generally at a location485 at the center of the aperture 483. Window 484 preferably is made ofa thin material which is transparent to IR radiation, such as HDPE,Silicon, Germanium or any other suitable material. Alternatively, otherappropriate window shapes, such as a rectangular window, may be used.

A substantial advantage of the use of a window 484 having a circularcross section is that such a window provides generally the sameradiation attenuation at side zones and at a center zone. In contrast,were a flat window to be placed at the aperture, it would providegreater attenuation at side zones than at a center zone.

The lens segments 415, 425, 435, 445, 455, 465 and 475 may be Fresnellenses, or cylindrical type lenses. Any other suitable type of lenselements, such as, for example, diffractive lenses and any suitablearrangement thereof, may be employed.

Alternatively, in other embodiments of the present invention, eachsub-detector may include multiple lens segments placed one above and/oralongside the other. This may be beneficial, for example, in achieving adenser coverage of the detection pattern, which enables a fasterresponse of the detector.

In alternative embodiments of the present invention, each sub-detectormay be associated with several lens segments, including lens segmentslying in the same vertical plane as well as lens segments lying in thesame horizontal row. For instance, a sub-detector could be associatedwith lens segments 415 and 425. This embodiment may be beneficial forinstance in cases where the number or density of the lens segmentswithin a horizontal row is relatively high and the horizontal anglebetween the sub fields-of-view of the lens segments is relatively small.In such cases it may be possible to reduce the cost of the detector byreducing the number of the sub-detectors, especially when the detectoris designed for outdoor environments having a moderate level of“undesired signals”.

As seen in FIGS. 12 and 13, each of sensors 410, 420, 430, 440, 450, 460and 470 of respective sub-detectors 416, 426, 436, 446, 456, 466 and 476is preferably located within a corresponding sub-detector compartment.The sub-detector compartments are designated respectively by referencenumerals 418, 428, 438, 448, 458, 468 and 478. Each sub-detectorcompartment is defined by walls, which may be similar to walls 284 ofFIG. 10, and which preferably have wall surfaces which are generallynon-reflective to both IR and visible light. Suitable walls may be madeof black plastic, which is preferably conditioned to minimize reflectionthereby. This arrangement allows each sensor to receive only radiationemanating from its corresponding sub field-of-view, as defined by thelens segment associated therewith.

Preferably, each sub-detector compartment is a sealed compartment thatprevents entry of air drafts and insects.

In accordance with a preferred embodiment of the present invention,sensors 410, 420, 430, 440, 450, 460 and 470 each comprise dual elementpyroelectric sensors, such as LHi-968 sensors, commercially availablefrom Perkin-Elmer of Freemont, Calif., USA.

It is a particular feature of the embodiment of FIGS. 12 and 13 that thenarrow slit type aperture 483 is provided. It is appreciated that all ofthe sub fields-of-view of each of sub-detectors 416, 426, 436, 446, 456,466 and 476 are positioned so that they intersect generally at onelocation centered at location 485. Preferably, aperture 483 is designedto frame location 485 as closely as possible without obstructing the subfields-of-view. A relatively narrow area surrounds location 485, justlarge enough to ensure that the housing surrounding aperture 483 doesnot obscure the sub fields-of-view of the sub-detectors.

A significant advantage of this structure, which includes a narrow slitaperture of minimal size, is that it drastically limits the amount ofsunlight and other visible light and thermal interference, which areknown in the art as common sources of false alarms. Additionally, thesmall window 484 is less likely to be accidentally or deliberatelydamaged, as is common in some public areas, such as schools.

A peripheral guard element 499 may be formed surrounding window 484 toprovide enhanced protection. The window 484 additionally may serve as aradiation filter, allowing only radiation of a certain wavelength range,such as IR radiation, to pass therethrough. The relatively narrow, smallsized window reduces the cost of the filter. Furthermore, it is easierto apply anti-masking measures to protect a narrow window, than toprotect a wide window.

Reference is now made to FIG. 14, which is a simplified pictorialillustration of a detector constructed and operative in accordance witha further preferred embodiment of the present invention, similar to thatof FIGS. 12 and 13 but employing mirrors instead of lenses, and to FIG.15, which is a simplified sectional illustration taken along sectionlines XV-XV in FIG. 14.

FIGS. 14 and 15 illustrate a mirror-based outdoor detector constructedand operative in accordance with a further preferred embodiment of thepresent invention. FIG. 14 is a general view of a detector comprisingseven sub-detectors, each sub-detector including a pyroelectric sensorassociated with one or more corresponding mirror elements, defining acorresponding sub field-of-view. Preferably, but not necessarily, theseven sub fields-of-view are not overlapping.

Preferably, the sub fields-of-view, corresponding to each of thesub-detectors, are substantially non-overlapping and are angled withrespect to each other, such that adjacent sub fields-of-view areseparated by no more than 30 degrees or by no more than 3 meters at theeffective far end of the corresponding sub fields-of-view, which isdetermined by the detector design. Such separation between adjacent subfields-of-view provides detection coverage of the field-of-view asrequired by various international standards, such as European standardTS 50131-2-2 and IEC-639-2-6, which require the detector to detect anintruder traversing a distance of three meters at certain angles anddirections. Each of the sub-detectors preferably views a portion of theentire field-of-view of the detector, such that the detector provides awide coverage area, for example, having a field-of-view divergence angleof 60 degrees or more.

As seen in FIGS. 14 and 15, the sub-detectors are arranged in a mutuallyconcave arrangement, so that each sensor is exclusively associated witha single mirror segment.

As seen in the illustrated embodiment, a sensor 510 is associated with amirror segment 512, defining a sub-detector 516. In a similar manner,sensors 520, 530, 540, 550, 560 and 570 are associated with respectivemirror segments 522, 532, 542, 552, 562 and 572 defining respectivesub-detectors 526, 536, 546, 556, 566 and 576.

As shown in FIGS. 14 and 15, sub-detectors 516, 526, 536, 546, 556, 566and 576 are arranged in a concave arrangement in a circular arc within ahousing element 580, thereby together to define the detector, which isdesignated by reference numeral 582.

The housing element defines a relatively narrow slit-type aperture 583adjacent which is preferably located a common window 584, preferablyhaving a circular cross-section with its center generally at a location585 at the center of aperture 583. Window 584 preferably is made of athin material transparent to IR radiation, such as HDPE, Silicon,Germanium or any other suitable material. Alternatively, otherappropriate window shapes, such as a rectangular slit, may be used.

A substantial advantage of the use of a window 584 having a circularcross section is that such a window provides generally the sameradiation attenuation at side zones and at a center zone. In contrast,were a flat window to be placed at the aperture, it would providegreater attenuation at side zones than at a center zone.

As seen in FIGS. 14 and 15, each of sensors 510, 520, 530, 540, 550, 560and 570 of respective sub-detectors 516, 526, 536, 546, 556, 566 and 576is preferably located within a corresponding sub-detector compartment.The sub-detector compartments may be defined by optional partialdividers which are designated respectively by reference numerals 515,525, 535, 545, 555 and 565. The partial dividers preferably havesurfaces which are generally non-reflective to both IR and visiblelight. Suitable dividers may be made of black plastic, which ispreferably conditioned to minimize reflection thereby. The optionaldividers provide some isolation between the sub fields-of-view of thesub-detectors, specifically from such interferences such as internalreflections from the internal walls of the detector and air drafts fromthe outside. The dividers must be of suitable length to provide theabove protection but limited in length so as not to interfere with thesub field-of-view of the neighboring sub-detector.

In accordance with a preferred embodiment of the present invention,sensors 510, 520, 530, 540, 550, 560 and 570 each comprise dual elementpyroelectric sensors such as LHi-968 sensors, commercially availablefrom Perkin-Elmer of Freemont, Calif., USA.

It is a particular feature of the embodiment of FIGS. 14 and 15 thatnarrow, slit type common aperture 583 is provided. It is appreciatedthat all of the sub fields-of-view of each of sub-detectors 516, 526,536, 546, 556, 566 and 576 are positioned so that they intersectgenerally at one location centered at location 585. Preferably, aperture583 is designed to frame location 585 as closely as possible withoutobstructing the sub fields-of-view. A relatively narrow area surroundslocation 585, just large enough to ensure that the housing surroundingaperture 583 does not obscure the sub fields-of-view of thesub-detectors.

One advantage of this structure, which includes a narrow slit-typeaperture of minimal size, is that it drastically limits the amount ofsunlight and other visible light and thermal interference, which areknown in the art as common sources of false alarms. Additionally, thenarrow window 584 is less likely to be accidentally or deliberatelydamaged, as is common in some public areas, such as schools.

Another advantage of the structure of the detector 582, is that due tothe small size of the window, one may apply anti-masking measuresthereto in a particularly effective manner. As seen in FIGS. 14 and 15,an emitter 590, such as an infrared LED, may be mounted within thedetector 582, to emit IR radiation in front of detector 582. An IRreceiver 594, such as a photo sensor, is preferably mounted within thedetector 582 facing window 584, such that it may receive the IRradiation emitted by emitter 590, reflected from just outside thedetector through window 584.

Typically, after suitable calibration over a predetermined calibrationtime duration, an object placed in front of window 584 or materialsprayed onto window 584 causing a change in the level of the reflectedIR radiation received by receiver 594, may be interpreted as a maskingattempt and may trigger an alarm. Anti-masking functionality of thistype is known, inter alia, from European Patents EP 0499177 and EP0481934, the disclosures of which are incorporated herein by reference.It is generally appreciated that this type of anti-masking functionalitydoes not always work well on relatively large detector windows.Accordingly, the provision of a relatively small window 584, as shown inFIGS. 14 and 15, enhances the effectiveness of this type of anti-maskingfunctionality.

It is a particular feature of this embodiment of the present invention,in which substantially all zones intersect at a relatively narrow window584, that any attempt to mask part of the window will not completelymask any given zone, as compared with the prior art, wherein it ispossible to completely mask a given zone by partial masking of a window.

A peripheral guard element 599 may be formed surrounding window 584 toprovide enhanced protection. The narrow window 584 may additionallyserve as a radiation filter, allowing only radiation of a certainwavelength range, such as IR radiation, to pass therethrough. Therelatively narrow, small sized aperture window 584 reduces the cost ofthe filter.

Reference is now made to FIG. 16, which is a simplified illustration ofa detector 600 constructed and operative in accordance with a stillfurther preferred embodiment of the present invention.

Detector 600 preferably comprises two sub-detectors, designated byreference numerals 602 and 604, having curtain-like sub fields-of-view,respectively designated by reference numerals 606 and 608. Thecurtain-like sub fields-of-view preferably generally extend through 90degrees from the vertical to the horizontal as shown. In thisembodiment, each of the sub fields-of-view 606 and 608 includes a singlezone. The sub-detectors 602 and 604 have a substantial horizontalseparation therebetween, which is preferably substantially larger thanthe focal lengths of optical elements associated with each of thesub-detectors 602 and 604. Optionally, detector 600 may include morethan two sub-detectors having a substantial horizontal separationtherebetween.

Detector 600 is operative to indicate when an intruder passes througheither one or both sub fields-of-view 606 and 608 according topredetermined criteria established by logic which is describedhereinbelow. Preferably, the two sub fields-of-view are arranged in agenerally parallel spaced mutual orientation. Alternatively, the two subfields-of-view are arranged in a non-parallel spaced mutual orientation.A certain amount of overlap may be provided between sub fields-of-view606 and 608.

Detector 600 preferably includes a housing 620 and a base 622 arrangedto be mounted on a vertical mounting wall 624 such that the base 622 isflush with the mounting wall 624. Housing 620 is preferably formed witha pair of generally downwardly inclined apertures, respectivelydesignated by reference numerals 632 and 634, which are arranged toextend generally horizontally along an aperture axis 635 in theorientation shown in FIG. 16. The housing 620 preferably includesrecessed housing panels 636 and 638 respectively disposed below windows632 and 634 so as not to interfere with passage of radiation into thewindows 632 and 634 in a generally vertical upward direction. Housing620 is preferably formed with a protruding central panel 640 disposedintermediate apertures 632 and 634 and corresponding panels 636 and 638.

Sub-detector 602 preferably comprises a pyroelectric sensor 642,disposed along the aperture axis 635, which receives radiation from subfield-of-view 606 via aperture 632 and via a reflecting surface 644which focuses the radiation onto sensor 642.

Reflecting surface 644 is preferably defined at least partially byrotation about aperture axis 635 of an off-axis portion, indicated byreference numeral 645, of a parabola, indicated by reference numeral 646in enlarged view II in FIG. 16, having an axis of symmetry, heredesignated by reference numeral 648, extending perpendicularly to theaperture axis 635 and having a focal point at the intersection of axes635 and 648. The pyroelectric sensor 642 is located generally at thefocal point. The parabola is rotated through an angle D which may beselected within a range of 0-180 degrees. Angle D corresponds to thedesired angular extent of the curtain-like sub field-of-view 606,preferably 90 degrees from the vertical to the horizontal as shown.Alternatively, smaller or larger angular extents of the curtain-like subfield-of-view 606 may possibly be defined by further rotation of theparabola.

The extent of portion 645 may remain constant as the parabola is rotatedthrough angle D or it may be varied. The variation may or may not belinear with rotation of the parabola.

By varying the extent of portion 645, the area of the reflecting surface644 which views certain portions of the sub field-of-view may be varied,thus correspondingly varying the sensitivity of the correspondingsub-detector 602 for those portions of the sub field-of-view. Thisvariation may be useful in various applications, such as for providingpet immunity by reducing sensitivity in regions close to the floor orfor ensuring uniformity of sensitivity along the extent of the curtainnotwithstanding distance from the sensor.

It is appreciated that variation of the area of the reflecting surface644 may additionally or alternatively be effected by masking selectedportions of the reflecting surface 644. The masking may be provided byan add-on device that can be fitted by the user in the field. Differentmasks having different sensitivity profiles may be provided, asappropriate for different applications of the detector.

Similarly, sub-detector 604 preferably comprises a pyroelectric sensor652, which receives radiation from sub field-of-view 608 via aperture634 and via a reflecting surface 654 which focuses the radiation ontosensor 652.

Reflecting surface 654 is preferably defined at least partially byrotation about aperture axis 635 of an off-axis portion of a parabola(not shown), having an axis of symmetry, here designated by referencenumeral 658, extending perpendicularly to the aperture axis 635 andhaving a focal point at the intersection of axes 635 and 658. Thepyroelectric sensor 652 is located generally at the focal point. Theparabola is rotated through an angle D which may be selected within arange of 0-180 degrees. Angle D corresponds to the desired angularextent of the curtain-like sub field-of-view 608, preferably 90 degreesfrom the vertical to the horizontal as shown. Alternatively, smaller orlarger angular extents of the curtain-like sub field-of-view 608 maypossibly be defined by further rotation of the parabola.

The extent of the portion of the parabola may remain constant as theparabola is rotated through angle D or it may be varied. The variationmay or may not be linear with rotation of the parabola.

By varying the extent of the portion of the parabola, the area of thereflecting surface 654 which views certain portions of the subfield-of-view may be varied, thus correspondingly varying thesensitivity of the corresponding sub-detector 604 for those portions ofthe sub field-of-view. This variation may be useful in variousapplications, such as for providing pet immunity by reducing sensitivityin regions close to the floor or for ensuring uniformity of sensitivityalong the extent of the curtain notwithstanding distance from thesensor.

It is appreciated that variation of the area of the reflecting surface654 may additionally or alternatively be effected by masking selectedportions of the reflecting surface 654. The masking may be provided byan add-on device that can be fitted by the user in the field. Differentmasks having different sensitivity profiles may be provided, asappropriate for different applications of the detector.

Each of the sub fields-of-view 606 and 608 diverges by an angle 2B whichdepends on the size of the pyroelectric sensing elements of sensors 642and 652 and the focal length of the reflecting surfaces 644 and 654, asexplained hereinbelow.

Overlapping between sub fields-of-view 606 and 608 can be eliminated orreduced by increasing the axial separation between the sub-detectors 602and 604 and/or by reducing the divergence angle 2B. Reducing the angle2B can be achieved by using reflecting surfaces 644 and 654 havingincreased focal lengths.

It is appreciated that the definition of reflecting surfaces 644 and 654by rotation of an off-axis portion of a parabola about aperture axis 635as described hereinabove obviates an increase in the depth of housing620, which would otherwise be required in order to accommodate anincrease in the focal lengths of the reflecting surfaces. Additionally,detector 600 requires only very narrow apertures, due to the use ofreflecting surfaces 644 and 654 defined as described above, andtherefore limits interference and is mechanically robust.

Preferably, in order to further minimize the length of the detectorhousing 620, the two sub-detectors 602 and 604 are configured such thatreflecting surfaces 644 and 654 reflect radiation from respective subfields-of-view 606 and 608 in mutually opposite directions alongpartially intersecting optical paths.

In a preferred embodiment of the invention, such as that shown in FIG.16, pyroelectric sensors 642 and 652 each comprise a dual elementpyroelectric sensor, such as an LHi-968, which is commercially availablefrom Perkin-Elmer of Freemont, Calif., USA.

In an alternative embodiment, one of the two sensing elements in each ofpyroelectric sensors 642 and 652 is covered. In this arrangement, eachof pyroelectric sensors 642 and 652 employs a single pyroelectricsensing element and may employ the covered sensing element for thermalcompensation as is known in the art. In this embodiment only half ofeach of sub fields-of-view 606 and 608 is provided.

As a further alternative, not shown, instead of using a dual elementpyroelectric sensor and covering one element, a single elementpyroelectric sensor may be used, such as SSAC10-11, commerciallyavailable from Nippon Ceramics Co. of Japan. Such single elementarrangements may perform better with longer focal lengths thandual-element arrangements in which the two fingers of each subfield-of-view are very close to each other, due to the longer focallength which may result in a reduced sensitivity of the dual elementsensors.

In the illustrated embodiment shown in FIG. 16, a curtain width d,typically 10 cm, may be achieved at a distance of 10 meters from thedetector 600.

According to an alternative embodiment of the present invention, anon-overlapping configuration may be employed to prevent false alarmsfrom sources of interference that influence only one sub field-of-viewor alternatively influence both sub fields-of-view simultaneously asexplained hereinabove with respect to multi sub-detector designs.

Adjustability of the azimuthal directions of one or both of the subfields-of-view may be achieved by corresponding azimuthal rotation ofthe reflecting surfaces 644 and 654. Alternatively, such adjustabilitymay be achieved by displacing the pyroelectric sensors 642 and 652towards or away from the base 622.

Reference is now made to FIG. 17, which is a simplified illustration ofa detector 700 constructed and operative in accordance with yet anotherpreferred embodiment of the present invention.

Detector 700 preferably comprises two sub-detectors, designated byreference numerals 702 and 704, having curtain-like sub fields-of-view,respectively designated by reference numerals 706 and 708. Thecurtain-like sub fields-of-view preferably generally extend through 90degrees from the vertical to the horizontal as shown. In thisembodiment, each of the sub fields-of-view 706 and 708 includes a singlezone. The sub-detectors 702 and 704 have a substantial horizontalseparation therebetween, which is preferably substantially larger thanthe focal lengths of optical elements associated with each of thesub-detectors 702 and 704. Optionally, detector 700 may include morethan two sub-detectors having a substantial horizontal separationtherebetween.

Detector 700 is operative to indicate when an intruder passes througheither one or both sub fields-of-view 706 and 708 according topredetermined criteria established by logic which is describedhereinbelow. Preferably, the two sub fields-of-view are arranged in agenerally parallel spaced mutual orientation. Alternatively, the two subfields-of-view are arranged in a non-parallel spaced mutual orientation.A certain amount of overlap may be provided between sub fields-of-view706 and 708.

Detector 700 preferably includes a housing 720 and a base 722 arrangedto be mounted on a vertical mounting wall 724 such that the base 722 isflush with the mounting wall 724. Housing 720 is preferably formed witha pair of generally downwardly inclined slit-like apertures,respectively designated by reference numerals 732 and 734, which arearranged to extend generally horizontally along an aperture axis 735 inthe orientation shown in FIG. 17. The housing 720 preferably includesrecessed housing panels 736 and 738 respectively disposed belowapertures 732 and 734 so as not to interfere with passage of radiationinto the apertures 732 and 734 in a generally vertical upward direction.

Sub-detector 702 preferably comprises a pyroelectric sensor 742, whichreceives radiation from sub field-of-view 706 via aperture 732 and via areflecting surface 744 which focuses the radiation onto sensor 742 viaat least one intermediate reflecting surface 745, which may or may nothave optical power.

Reflecting surface 744 is preferably defined at least partially byrotation about aperture axis 735 of an off-axis portion, indicated byreference numeral 746, of a parabola, indicated by reference numeral 747in enlarged view II in FIG. 17. Parabola 747 has an axis of symmetry,here designated by reference numeral 748, which extends perpendicularlyto the aperture axis 735, and having a focal point at the intersectionof axes 735 and 748. The pyroelectric sensor 742 may be located at anysuitable location within housing 720 and the at least one intermediatereflecting surface 745, here shown as a single intermediate reflectingsurface, is located along the optical path defined by reflecting surface744 at a location suitable for redirecting radiation from reflectingsurface 744 to pyroelectric sensor 742.

The parabola 747 is rotated through an angle D which may be selectedwithin a range of 0-180 degrees. Angle D corresponds to the desiredangular extent of the curtain-like sub field-of-view 706, preferably 90degrees from the vertical to the horizontal as shown. Alternatively,smaller or larger angular extents of the curtain-like sub field-of-view706 may possibly be defined by further rotation of the parabola 747.

The extent of portion 746 may remain constant as the parabola 747 isrotated through angle D or it may be varied. The variation may or maynot be linear with rotation of the parabola 747.

By varying the extent of portion 746, the area of the reflecting surface744 which views certain portions of the sub field-of-view may be varied,thus correspondingly varying the sensitivity of the correspondingsub-detector 702 for those portions of the sub field-of-view. Thisvariation may be useful in various applications, such as for providingpet immunity by reducing sensitivity in regions close to the floor orfor ensuring uniformity of sensitivity along the extent of the curtainnotwithstanding distance from the sensor.

It is appreciated that variation of the area of the reflecting surface744 may additionally or alternatively be effected by masking selectedportions of the reflecting surface 744. The masking may be provided byan add-on device that can be fitted by the user in the field. Differentmasks having different sensitivity profiles may be provided, asappropriate for different applications of the detector.

Similarly, sub-detector 704 preferably comprises a pyroelectric sensor752, which receives radiation from sub field-of-view 708 via aperture734 and via a reflecting surface 754 which focuses the radiation ontosensor 752 via at least one intermediate reflecting surface 755, whichmay or may not have optical power.

Reflecting surface 754 is preferably defined at least partially byrotation about aperture axis 735 of an off-axis portion of a parabola(not shown), having an axis of symmetry, here designated by referencenumeral 758, extending perpendicularly to the aperture axis 735, and afocal point at the intersection of axes 735 and 758. The pyroelectricsensor 752 may be located at any suitable location within housing 720and the at least one intermediate reflecting surface 755, here shown asa single intermediate reflecting surface is located along the opticalpath defined by reflecting surface 754 at a location suitable forredirecting radiation from reflecting surface 754 to pyroelectric sensor752.

The parabola is rotated through an angle D which may be selected withina range of 0-180 degrees. Angle D corresponds to the desired angularextent of the curtain-like sub field-of-view 708, preferably 90 degreesfrom the vertical to the horizontal as shown. Alternatively, smaller orlarger angular extents of the curtain-like sub field-of-view 708 maypossibly be defined by further rotation of the parabola.

The extent of the portion of the parabola may remain constant as theparabola is rotated through angle D or it may be varied. The variationmay or may not be linear with rotation of the parabola.

By varying the extent of the portion of the parabola, the area of thereflecting surface 754 which views certain portions of the field-of-viewmay be varied, thus correspondingly varying the sensitivity of thecorresponding sub-detector 702 for those portions of the field-of-view.This variation may be useful in various applications, such as forproviding pet immunity by reducing sensitivity in regions close to thefloor or for ensuring uniformity of sensitivity along the extent of thecurtain notwithstanding distance from the sensor.

It is appreciated that variation of the area of the reflecting surface754 may additionally or alternatively be effected by masking selectedportions of the reflecting surface 754. The masking may be provided byan add-on device that can be fitted by the user in the field. Differentmasks having different sensitivity profiles may be provided, asappropriate for different applications of the detector.

Each of the sub fields-of-view 706 and 708 diverges by an angle 2B whichdepends on the size of the pyroelectric sensing elements of sensors 742and 752 and the focal length of the reflecting surfaces 744 and 754, asexplained hereinbelow.

Overlapping between sub fields-of-view 706 and 708 can be eliminated orreduced by increasing the axial separation between the sub-detectors 702and 704 and/or by reducing the divergence angle 2B. Reducing the angle2B can be achieved by using reflecting surfaces 744 and 754 havingincreased focal lengths.

It is appreciated that the definition of reflecting surfaces 744 and 754by rotation of an off-axis portion of a parabola about aperture axis 735as described hereinabove, obviates an increase in the depth of housing720, which would otherwise be required in order to accommodate anincrease in the focal lengths of the reflecting surfaces. Additionally,detector 700 requires only very narrow apertures due to the use ofreflecting surfaces 744 and 754 defined as described above, andtherefore limits interference and is mechanically robust.

Preferably, in order to further minimize the length of the detectorhousing 720, the two sub-detectors 702 and 704 are configured such thatreflecting surfaces 744 and 754 reflect radiation from respective subfields-of-view 706 and 708 in mutually opposite directions alongpartially intersecting optical paths.

In a preferred embodiment of the invention, such as that shown in FIG.17, pyroelectric sensors 742 and 752 each comprise a dual elementpyroelectric sensor, such as an LHi-968, which is commercially availablefrom Perkin-Elmer of Freemont, Calif., USA.

In an alternative embodiment, one of the two sensing elements in each ofpyroelectric sensors 742 and 752 is covered. In this arrangement, eachof pyroelectric sensors 742 and 752 employs a single pyroelectricsensing element and may employ the covered sensing element for thermalcompensation as is known in the art. In this embodiment only half ofeach of sub fields-of-view 706 and 708 is provided.

As a further alternative, not shown, instead of using a dual elementpyroelectric sensor and covering one element, a single elementpyroelectric sensor may be used, such as SSAC10-11, commerciallyavailable from Nippon Ceramics Co. of Japan. Such single elementarrangements may perform better with longer focal lengths thandual-element arrangements in which the two fingers of each subfield-of-view are very close to each other due to the longer focallength which may result in a reduced sensitivity of the dual elementsensors.

In the illustrated embodiment shown in FIG. 17, a curtain width d,typically 10 cm, may be achieved at a distance of 10 meters from thedetector 700.

According to an alternative embodiment of the present invention, anon-overlapping configuration may be employed to prevent false alarmsfrom sources of interference that influence only one sub field-of-viewor alternatively influence both sub fields-of-view simultaneously asexplained hereinabove with respect to multi sub-detector designs.

Adjustability of the azimuthal directions of one or both of the subfields-of-view may be achieved by corresponding azimuthal rotation ofthe reflecting surfaces 744 and 754. Alternatively, such adjustabilitymay be achieved by displacing the pyroelectric sensors 742 and 752towards or away from the base 722.

Reference is now made to FIG. 18, which is a simplified illustration ofprocessing of a signal indicative of a typical human intrusion sensed bya detector 800, of the type described hereinabove with respect to FIGS.16 and 17, comprising two dual-element sub-detectors, designated byreference numerals 802 and 804, having respective curtain-like subfields-of-view 806 and 808, each including a single zone.

The passage of a person sequentially through respective curtain-like subfields-of-view 808 and 806, generally as shown in FIG. 18, produces apair of bi-polar signals, respectively designated by reference numerals810 and 812, which are separated in time. In signals 810 and 812, thepositive and negative peaks correspond to the crossing of the centers ofthe fingers of the sub fields-of-view.

The designation “T” denotes the time separation between respectivepositive peaks of signals 810 and 812. The designation “t_(n)” denotesthe time separation between respective positive and negative peaks ofeach of signals 810 and 812 which corresponds to the time it takes aperson to traverse the distance d, the time separation betweenrespective positive and negative peaks of signal 810 being designated t₁and the time separation between respective positive and negative peaksof signal 812 being designated as t₂. The designation “t” is used todenote a function, such as a mean or average of t_(n), of varioussignals.

Signals 810 and 812 are supplied to computation circuitry 814 of thedetector 800, which is programmed with the following structuralparameters. As will be described hereinbelow, the following parametersare preferably used in signal processing logic of the detector 800.

X—the distance between the centers of sub fields-of-view 806 and 808 atthe detector 800;

A—the angle between the centers of adjacent sub fields-of-view 806 and808;

2B—angle between the centers of fingers in each of sub fields-of-view806 and 808.

As described hereinbelow, computation circuitry 814 is operative tocalculate a parameter Z₀/t, which is a metric of intruder speed, basedon the above structural parameters X, A and 2B and on the movement of aperson. If it is assumed that the person traverses the subfields-of-view 808 and 806 at a fixed speed and at a fixed distance fromthe detector 800, Z₀/t becomes a constant K, for given structuralparameters of the detector and independent of the speed of movement ofthe person, and is expressed as follows:K=tan(A/2)/tan(B)  (1)

The derivation of equation (1) is shown hereinbelow with reference toequation (11).

Computation circuitry 814 is operative to calculate the followingparameters based on the signals 810 and 812 and the above structuralparameters X, A and 2B:

R, the distance of the person from detector 800 along a centerline 816between sub fields-of-view 806 and 808;

V, the speed of the person as he traverses the sub fields-of-view 806and 808;

t₁/t₂, the quotient of the time separations between respective positiveand negative peaks of respective signals 810 and 812.

Z₀, the period of time at which the person traverses the distancebetween the sub fields-of-view 808 and 806 at distance R from detector800, less X, the distance between the centers of sub fields-of-view 806and 808 at the detector 800.

Z₀/t, the quotient of Z₀ divided by t.

In order to do so, the computation circuitry 814 employs the followingcalculated parameters:

D, the distance between the centers of the sub fields-of-view 806 and808 at distance R from detector 800; and

d, the distance between the centers of the respective fingers of eachsub-field-of-view, corresponding to angle 2B, at distance R fromdetector 800.

Under the assumption that a person traverses the sub fields-of-view at afixed speed and at a fixed distance from the detector 800, thecomputation circuitry 814 preferably employs the following equations:d=2·R·tan(B)  (2)t=0.5·t ₁+0.5·t ₂ =d/V=[2·R·tan(B)]/V  (3)D=X+2·R·tan(A/2)  (4)T=D/V=[X+2·R·tan(A/2)]/V  (5)

Division of equation (3) by equation (5) yields:t/T=[2·tan(B)]/[X/R+2·tan(A/2)]  (6)

Inasmuch as R is the only unknown in equation (6), and assuming that thedistance R is constant, one can rewrite equation (6) as follows:R=X·t/{2·[T·tan(B)−t·tan(A/2)]}  (7)

Under the assumption that R and V are constant, V can be derived from Rby rewriting equation (5) as follows:V=[X+2·R·tan(A/2)]/T  (8)

t₁/t₂, the quotient of the time separations between respective positiveand negative peaks of respective signals 810 and 812, which representsthe ratio of the speeds V of the person traversing sub fields-of-view806 and 808 assuming that the range R is constant, is calculated basedon measured values of t₁ and t₂.

Z₀ can be derived from R and V by rewriting equation (4) as follows:Z ₀ =[D−X]/V=[2·R·tan(A/2)]/V  (9)

The quotient Z₀/t is derived from equation 9, as follows:Z ₀ /t=[2·R·tan(A/2)]/V·(0.5·t ₁+0.5·t ₂)  (10)

Assuming the person traverses the sub fields-of-view 806 and 808 at afixed speed V and at a fixed distance R from the detector, the parametert, derived in equation (3), may be used to derive the parameter K asshown hereinabove in equation (1), as follows:Z ₀ /t={[2·R·tan(A/2)]/V}/{[2·R·tan(B)]/V}=tan(A/2)/tan(B)=K  (11)

It is desired to employ the computed parameters R, V, t₁/t₂ and Z₀/t inorder to eliminate or reduce false alarms. Accordingly, followingcalculation of parameters R, V, t₁/t₂ and Z₀/t, suitable thresholds areapplied to each of the parameters and/or to combinations thereof inorder to distinguish signals characteristic of intruders from spurioussignals.

For example, considering the parameter V, any object moving faster thenan upper speed threshold, such as 3 meters per second, or slower than alower speed threshold, such as 0.1 meters per second, will not beconsidered an intruder. Other speed thresholds may be selected asappropriate, for example, according to standards or as otherwise knownin the art.

It is also possible to define a specific range for the parameter R, suchas a range of 2 to 30 meters. Any object moving in a region lyingoutside these limits may be considered not to be an intruder.

If a person traverses the sub fields-of-view 806 and 808 at the samespeed, the ratio t₁/t₂ will equal 1. It may be assumed that an intrudermay change the speed of his motion between the two sub fields-of-view toa certain degree, for instance 0.5<t₁/t₂<2.0. Accordingly, any value fort₁/t₂ lying outside of this range may be considered not to represent anintruder. Any other suitable range for t₁/t₂ may be selected inaccordance with the specific design and application of the detector.

If a person traverses the sub fields-of-view 806 and 808 and thedistance therebetween at a fixed speed and at a fixed distance fromdetector 800, the ratio (Z₀/t)/K equals 1. The quotient (Z₀/t)/K may beused as an indication of the extent that an intruder changes his speedof motion during the traversal of the distance D.

It may be assumed that a person may change the speed of his motionbetween the two sub fields-of-view to a certain extent, for instance0.7<(Z₀/t)/K<1.5. Accordingly any value for Z₀/t/K lying outside of thisrange may be considered not to represent an intruder. Any other suitablerange for (Z₀/t)/K may be selected in accordance with the specificdesign and application of the detector.

Additionally, if a person traverses the sub fields-of-view 806 and 808and the distance therebetween at a fixed speed and at a fixed distancefrom detector 800, the ratio [t₁/t₂]/[(Z₀/t)/K] also equals 1. The ratio[t₁/t₂]/[(Z₀/t)/K] may be used as another indication of the extent thatan intruder changes his speed of motion during the traversal of thedistance D.

It may be assumed that a person may change the speed of his motionbetween the two sub fields-of-view to a certain extent, for instance0.8<[t₁/t₂]/[(Z₀/t)/K]<1.3. Accordingly any value for [t₁/t₂]/[(Z₀/t)/K]lying outside of this range may be considered not to represent anintruder. Any other suitable range for [t₁/t₂]/[(Z₀/t)/K] may beselected in accordance with the specific design and application of thedetector.

Application of the above thresholds to respective parameters R, V,t₁/t₂, Z₀/t/K and [t₁/t₂]/[(Z₀/t)/K] preferably provides outputs toalarm logic circuitry 818. Alarm logic circuitry also receives inputsfrom traversal logic circuitry 820 which indicates the direction ofmotion through sub fields-of-view 806 and 808, i.e. which of the subfields-of-view 806 and 808 is traversed initially. Logic circuitry 818makes a false-alarm determination when the inputs thereto are notcharacteristic of an intruder. The output of logic circuitry 818 is analarm enable or disable signal.

The foregoing description of FIG. 18 is also applicable to a situationwhere the two fields-of-view are parallel. In such a case:D=X  (12)d=2·R·tan(B)  (13)t=d/V=[2·R·tan(B)]/V  (14)T=D/V=X/V  (15)

Division of formula (14) by formula (15) gives:t/T=[2·R·tan(B)]/X  (16)

As can be seen, in the parallel embodiment it is also possible todetermine the range R from formula (16) and the speed V from formula(15).R=[t·x]/[2·T·tan(B)]  (17)V=X/T  (18)

The computed parameters R, V, t₁/t₂, Z₀/t/K and [t₁/t₂]/[(Z₀/t)/K] andthe thresholds described hereinabove are also applicable to anembodiment wherein the sub fields-of-view are parallel.

The description of FIG. 18 for cases where A does not equal zero is alsoapplicable to adjacent sub fields-of-view of detectors having multiplesub fields-of-view embodiments, such as those described hereinabove withreference to FIGS. 1-6 and 10-15. For example, in the detectors of FIGS.3 and 6 the azimuthal diverging angle A between the respective subfields-of-view 87 and 88 (FIG. 3) and 187 and 188 (FIG. 6),respectively, is equivalent to the angle A in FIG. 18. Similarly thehorizontal diverging angle 2B between the centers 98 (FIG. 3) and 198(FIG. 6) of the two fingers of each dual element sub field-of-view 87and 88 (FIG. 3) and 187 and 188 (FIG. 6) in the detectors of respectiveFIGS. 3 and 6 is equivalent to the angle 2B in FIG. 18.

It is appreciated that the distance between the two sensors 60 and 70 indetector 82 of FIGS. 1-3 is very small relative to the distances R and Din FIG. 18 and therefore can be considered as being equal to zero.Therefore, the above formulas 1 to 5 may be employed, setting X=0, toanalyze the signals of each two adjacent sub detectors, such asdetectors 10, 20, 30, 40, 50, 60 and 70 of FIGS. 1-3 or detectors 110,120, 130, 140, 150, 160 and 170 of FIGS. 4-6, and accordingly to decidewhether the detected signals correspond to a moving intruder or tointerference, thereby further improving the false alarm immunity of thedetector.

Reference is now made to FIG. 19, which is a simplified illustration ofprocessing of a signal indicative of a typical human intrusion sensed bya detector 900, of the type described hereinabove with respect to FIGS.16 and 17, having two single-element sub-detectors, designated byreference numerals 902 and 904, having respective curtain-like subfields-of-view 906 and 908, each including a single zone.

The passage of a person sequentially through respective curtain-like subfields-of-view 906 and 908, generally as shown in FIG. 19, produces apair of signals, respectively designated by reference numerals 910 and912, which are separated in time.

The designation “T” denotes the time separation between respectivepositive peaks of signals 910 and 912. The designation “t_(n)” denotesthe time separation between respective approximated zero crossings ofeach of signals 910 and 912 which corresponds to the time it takes aperson to traverse the distance d, the time separation betweenrespective approximated zero crossings of signal 910 being designated t₁and the time separation between respective approximated zero crossingsof signal 912 being designated as t₂. The designation “t” is used todenote a function, such as a mean or average of t_(n), of varioussignals.

Signals 910 and 912 are supplied to computation circuitry 914 of thedetector 900, which is programmed with the following structuralparameters. As will be described hereinbelow, the following parametersare used in signal processing logic of the detector 900.

X—the distance between the centers of sub fields-of-view 906 and 908 atthe detector 900;

A—the angle between the centers of adjacent sub fields-of-view 906 and908;

2B—angle between the edges of each of sub fields-of-view 906 and 908.

As described hereinbelow, computation circuitry 914 is operative tocalculate a parameter Z₀/t, which is a metric of intruder speed, basedon the above structural parameters X, A and 2B and on the movement of aperson. If it is assumed that the person traverses the subfields-of-view 906 and 908 at a fixed speed and at a fixed distance fromthe detector 900, Z₀/t becomes a constant K, for given structuralparameters of the detector and independent of the speed of movement ofthe person, and is expressed as follows:K=tan(A/2)/tan(B)  (19)

The derivation of equation (19) is shown hereinbelow with reference toequation (29).

Computation circuitry 914 is operative to calculate the followingparameters based on the signals 910 and 912 and the above structuralparameters X, A and 2B:

R, the distance of the person from detector 900 along a centerline 916between sub fields-of-view 906 and 908;

V, the speed of the person as he traverses the sub fields-of-view 906and 908;

t₁/t₂, the quotient of the time separations between respectiveapproximated zero crossings of respective signals 910 and 912.

Z₀, the period of time at which the person traverses the distancebetween the sub fields-of-view 906 and 908 at distance R from detector900, less X, the distance between the centers of sub fields-of-view 906and 908 at the detector 900.

Z₀/t, the quotient of Z₀ divided by t.

In order to do so, the computation circuitry 914 employs the followingcalculated parameters:

D, the distance between the centers of the sub fields-of-view 906 and908 at distance R from detector 900; and

d, the distance between the edges of each sub field-of-view,corresponding to angle 2B, at distance R from detector 900.

Under the assumption that a person traverses the sub fields-of-view at afixed speed and at a fixed distance from the detector 900, thecomputation circuitry 914 preferably employs the following equations:d=2·R·tan(B)  (20)t=0.5·t ₁+0.5·t ₂ =d/V=[2·R·tan(B)]/V  (21)D=X+2·R·tan(A/2)  (22)T=D/V=[X+2·R·tan(A/2)]/V  (23)

Division of equation (21) by equation (23) yields:t/T=[2·tan(B)]/[X/R+2·tan(A/2)]  (24)

Inasmuch as R is the only unknown in equation (24), and assuming thatthe distance R is constant, one can rewrite equation (24) as follows:R=X t/{2·[T·tan(B)−t·tan(A/2)]}  (25)

Under the assumption that R and V are constant, V can be derived from Rby rewriting equation (23) as follows:V=[X+2·R·tan(A/2)]/T  (26)

t₁/t₂, the quotient of the time separations between respectiveapproximated zero crossings of respective signals 910 and 912, whichrepresents the ratio of the speeds V of the person traversing subfields-of-view 906 and 908 assuming that the range R is constant, iscalculated based on measured values of t₁ and t₂.

Z₀ can be derived from R and V by rewriting equation (22) as follows:Z ₀ =[D−X]/V=[2·R·tan(A/2)]/V  (27)

The quotient Z₀/t is derived from equation 27, as follows:Z ₀ /t=[2·R·tan(A/2)]/V·(0.5·t ₁+0.5·t ₂)  (28)

Assuming the person traverses the sub fields-of-view 906 and 908 at afixed speed V and at a fixed distance R from the detector, the parametert, derived in equation (21), may be used to derive the parameter K shownabove in equation (19), as follows:Z ₀ /t={[2·R·tan(A/2)]/V}/{[2R·tan(B)]/V}=tan(A/2)/tan(B)=K   (29)

It is desired to employ the computed parameters R, V, t₁/t₂ and Z₀/t inorder to eliminate or reduce false alarms. Accordingly, followingcalculation of parameters R, V, t₁/t₂ and Z₀/t, suitable thresholds areapplied to each of the parameters and/or to combinations thereof inorder to distinguish signals characteristic of intruders from spurioussignals.

For example. considering the parameter V, any object moving faster thenan upper speed threshold, such as 3 meters per second, or slower than alower speed threshold, such as 0.1 meters per second, will not beconsidered an intruder. Other speed thresholds may be selected asappropriate, for example, according to standards or as otherwise knownin the art.

It is also possible to define a specific range for the parameter R, suchas a range of 2 to 30 meters. Any object moving in a region lyingoutside these limits may be considered not to be an intruder.

If a person traverses the sub fields-of-view 906 and 908 at the samespeed, the ratio t₁/t₂ will equal 1. It may be assumed that an intrudermay change the speed of his motion between the two sub fields-of-view toa certain degree, for instance 0.5<t₁/t₂<2.0. Accordingly, any value fort₁/t₂ lying outside of this range may be considered not to represent anintruder. Any other suitable range for t₁/t₂ may be selected inaccordance with the specific design and application of the detector.

If a person traverses the sub fields-of-view 906 and 908 and thedistance therebetween at a fixed speed and at a fixed distance fromdetector 900, the ratio (Z₀/t)/K equals 1. The quotient (Z₀/t)/K may beused as an indication of the extent that an intruder changes his speedof motion during the traversal of the distance D.

It may be assumed that a person may change the speed of his motionbetween the two sub fields-of-view to a certain extent, for instance0.7<(Z₀/t)/K<1.5. Accordingly any value for Z₀/t/K lying outside of thisrange may be considered not to represent an intruder. Any other suitablerange for (Z₀/t)/K may be selected in accordance with the specificdesign and application of the detector.

Additionally, if a person traverses the sub fields-of-view 906 and 908and the distance therebetween at a fixed speed and at a fixed distancefrom detector 900, the ratio [t₁/t₂]/[(Z₀/t)/K] also equals 1. The ratio[t₁/t₂]/[(Z₀/t)/K] may be used as another indication of the extent thatan intruder changes his speed of motion during the traversal of thedistance D.

It may be assumed that a person may change the speed of his motionbetween the two sub fields-of-view to a certain extent, for instance0.8<[t₁/t₂]/[(Z₀/t)/K]<1.3. Accordingly any value for [t₁/t₂]/[(Z₀/t)/K]lying outside of this range may be considered not to represent anintruder. Any other suitable range for [t₁/t₂]/[(Z₀/t)/K] may beselected in accordance with the specific design and application of thedetector.

Application of the above thresholds to respective parameters R, V,t₁/t₂, Z₀/t/K and [t₁/t₂]/[(Z₀/t)/K] preferably provides outputs toalarm logic circuitry 918. Alarm logic circuitry 918 also receivesinputs from traversal logic circuitry 920 which indicates the directionof motion through sub fields-of-view 906 and 908, i.e. which of the subfields-of-view 906 and 908 is traversed initially. Alarm logic circuitry918 makes a false-alarm determination when the inputs thereto are notcharacteristic of an intruder. The output of alarm logic circuitry 918is an alarm enable or disable signal.

The foregoing description of FIG. 19 is applicable to a situation wherethe two fields-of-view are parallel. In such a case:D=X  (30)d=2·R·tan(B)  (31)t=d/V=[2·R·tan(B)]/V  (32)T=D/V=X/V  (33)

Division of formula (32) by formula (33) gives:t/T=[2·R·tan(B)]/X  (34)

As can be seen, in the parallel embodiment it is also possible todetermine the range R from formula (34) and the speed V from formula(33).R=[t·x]/[2·T·tan(B)]  (35)V=X/T  (36)

The computed parameters R, V, t₁/t₂, Z₀/t/K and [t₁/t₂]/[(Z₀/t)/K] andthe thresholds described hereinabove are also applicable to anembodiment wherein the sub fields-of-view are parallel.

The description of FIG. 19 for cases where A does not equal zero is alsoapplicable to adjacent sub fields-of-view of single element detectorshaving multiple sub fields-of-view.

Reference is now made to FIG. 20, which is a flow chart illustrating apreferred embodiment of directional logic particularly useful in theembodiments of FIGS. 16-19. This directional logic may be incorporated,for example, as part of the computation circuitry in the embodiments ofFIGS. 18 and 19 or may be added to the apparatus shown in FIGS. 16 and17. The directional logic preferably employs inputs from traversal logicsuch as traversal logic 820 (FIG. 18) which indicates the order in whichtwo or more fields-of-view, such as sub fields-of-view 806 and 808 (FIG.18), are traversed.

As seen in FIG. 20, a function selector may be provided for enabling auser to select from one or more operational modes of a detector, such asdetector 600 shown in FIG. 16 or detector 700 shown in FIG. 17.

In a first operational mode, an alarm may be enabled once one of the twosub fields-of-view, here termed “curtains”, is traversed in eitherdirection.

In a second operational mode, an alarm is enabled only once both subfields-of-view are traversed in either direction.

In a third operational mode, an alarm may be enabled once both subfields-of-view are traversed in a first direction, such as when enteringa room. The alarm is not enabled when one or both sub fields-of-view aretraversed in the opposite direction, for example when exiting the room.

In a fourth operational mode, when a person traverses both subfields-of-view in a first direction, such as exiting a room, the alarmis not activated. However, such traversal activates a timer, whichdefines a predetermined time duration during which the subfields-of-view may be traversed in the opposite direction, such asre-entering the room, without activating the alarm. Optionally, anaudible and/or visual indication may be provided during thepredetermined time duration.

When a person traverses both sub fields-of-view in a second direction,which is opposite to the first direction, such as when entering a room,the detector determines whether the predetermined time duration haselapsed. If the time duration has not elapsed, the timer is turned offand an alarm is disabled. If the time duration has elapsed, an alarm isenabled.

It is appreciated that the predetermined time duration may be selectedor adjusted by the user, preferably according to the requirements of theenvironment in which the detector is installed.

Reference is now made to FIG. 21, which is a simplified pictorialillustration of a mirror-based detector constructed and operative inaccordance with a further preferred embodiment of the present invention.As seen in FIG. 21, the detector typically includes a mirror havingfourteen mirror segments, each defining a corresponding zone. The mirrorsegments are arranged in a mutually concave arrangement in two rows.

As seen in the illustrated embodiment, a sensor 1010 is associated withmirror segments 1012, 1014, 1016, 1018, 1020, 1022 and 1024 in a top rowand with mirror segments 1032, 1034, 1036, 1038, 1040, 1042 and 1044 ina bottom row. Each of the mirror segments is operative to focusradiation from its corresponding zone onto the sensor 1010. The mirrorsegments 1012, 1014, 1016, 1018, 1020, 1022 and 1024 preferably arearranged in a concave arrangement in a circular arc within a housingelement 1050. Similarly, mirror segments 1032, 1034, 1036, 1038, 1040,1042 and 1044 preferably are arranged in a concave arrangement in acircular arc within housing element 1050.

The housing element 1050 defines a relatively narrow slit aperture 1052adjacent which is preferably located a common window 1054, preferablyhaving a circular cross-section with its center generally at a location1056 at the center of aperture 1052. Window 1054 preferably is made of athin material transparent to IR radiation, such as HDPE, Silicon,Germanium or any other suitable material. Alternatively, otherappropriate window shapes may be used.

A substantial advantage of the use of a window 1054 having a circularcross section is that such a window provides generally the sameradiation attenuation at side zones and at a center zone. In contrast,were a flat window to be placed at the aperture, it would providegreater attenuation at side zones than at a center zone.

Sensor 1010 preferably comprises a dual element pyroelectric sensor,such as a LHi-968 sensor, commercially available from Perkin-Elmer ofFreemont, Calif., USA.

It is a particular feature of the embodiment of FIG. 21 that narrow,slit type common aperture 1052 is provided. It is appreciated that allof the zones defined by each single horizontal layer of mirror segmentsare positioned so that they intersect generally at one location centeredat location 1056. Preferably, aperture 1052 is designed to framelocation 1056 as closely as possible without obstructing the zones. Arelatively narrow area surrounds location 1056 just large enough toensure that the housing surrounding aperture 1052 does not obscure thezones.

The advantages of the use of a narrow aperture housing structure aredescribed hereinabove with reference to the embodiments shown in FIGS.12-17.

Reference is now made to FIG. 22, which is a simplified pictorialillustration of a mirror-based detector constructed and operative inaccordance with a further preferred embodiment of the present invention.As seen in FIG. 22, the detector typically includes a mirror havingfourteen mirror segments, each defining a corresponding zone. The mirrorsegments are arranged in a mutually concave arrangement in two rows.

As seen in the illustrated embodiment, a sensor 1060 is associated withmirror segments 1062, 1064, 1066, 1068, 1070, 1072 and 1074 in a top rowand with mirror segments 1076, 1078, 1080, 1082, 1084, 1086 and 1088 ina bottom row. Each of the mirror segments is operative to focusradiation from its corresponding zone onto the sensor 1060 via at leastone intermediate reflecting surface 1090. The mirror segments 1062,1064, 1066, 1068, 1070, 1072 and 1074 preferably are arranged in aconcave arrangement in a circular arc within a housing element 1092.Similarly, mirror segments 1076, 1078, 1080, 1082, 1084, 1086 and 1088preferably are arranged in a concave arrangement in a circular arcwithin housing element 1092.

The sensor 1060 may be located at any suitable location within thehousing 1092. The at least one intermediate reflecting surface 1090,here shown as a single intermediate reflecting surface, is located alongoptical paths defined by mirror segments 1062, 1064, 1066, 1068, 1070,1072, 1074, 1076, 1078, 1080, 1082, 1084, 1086 and 1088 at a locationsuitable for redirecting radiation from the mirror segments topyroelectric sensor 1060.

In the illustrated embodiment of FIG. 22, the sensor 1060 is shownmounted at an aperture 1093 in mirror segment 1068. It is appreciatedthat alternatively, the sensor 1060 may be located rearwardly of theaperture, and in such a case may be mounted on a circuit board (notshown) which also mounts the mirror segments. In such a case,intermediate reflecting surface 1090 may require some optical power.

The housing element 1092 defines a relatively narrow slit aperture 1094adjacent which is preferably located a common window 1096, preferablyhaving a circular cross-section with its center generally at a location1098 at the center of aperture 1094. Window 1096 preferably is made of athin material transparent to IR radiation, such as HDPE, Silicon,Germanium or any other suitable material. Alternatively, otherappropriate window shapes, such as a flat window, may be used.

A substantial advantage of the use of a window 1096 having a circularcross section is that such a window provides generally the sameradiation attenuation at side zones and at a center zone. In contrast,were a flat window to be placed at the aperture, it would providegreater attenuation at side zones than at a center zone.

Sensor 1060 preferably comprises a dual element pyroelectric sensor,such as a LHi-968 sensor, commercially available from Perkin-Elmer ofFreemont, Calif., USA.

It is a particular feature of the embodiment of FIG. 22 that narrow,slit type common aperture 1094 is provided. It is appreciated that allof the zones defined by each single horizontal layer of mirror segmentsare positioned so that they intersect generally at one location centeredat location 1098. Preferably, aperture 1094 is designed to framelocation 1098 as closely as possible without obstructing the zones. Arelatively narrow area surrounds location 1098, just large enough toensure that the housing surrounding aperture 1094 does not obscure thezones.

The advantages of the use of a narrow aperture housing structure aredescribed hereinabove with reference to the embodiments shown in FIGS.12-17.

Reference is now made to FIG. 23, which is a simplified illustration ofa detector 1100 constructed and operative in accordance with a yet afurther preferred embodiment of the present invention.

Detector 1100 preferably provides a curtain-like field-of-view,designated by reference numerals 1102. The curtain-like field-of-viewpreferably generally extends through 90 degrees from the vertical to thehorizontal as shown.

Detector 1100 preferably includes a housing 1120 and a base 1122arranged to be mounted on a vertical mounting wall 1124 such that thebase 1122 is flush with the mounting wall 1124. Housing 1120 ispreferably formed with a generally downwardly inclined slit-likeaperture, designated by reference numeral 1126, which is arranged toextend generally horizontally along a slit axis 1128 in the orientationshown in FIG. 23. The housing 1120 preferably includes a recessedhousing panel 1130 disposed below a window 1132 located at aperture1126. The recess is provided so as not to interfere with passage ofradiation into aperture 1126 in a generally vertical upward direction.Housing 1120 is preferably formed with a protruding top panel 1140disposed above window 1132.

Window 1132 preferably is made of a thin material transparent to IRradiation, such as HDPE, Silicon, Germanium or any other suitablematerial, and preferably has a circular cross-section with its centergenerally at the center of aperture 1126.

A substantial advantage of the use of a window 1132 having a circularcross section is that such a window provides generally the sameradiation attenuation at side zones and at a center zone. In contrast,were a flat window to be placed at the aperture, it would providegreater attenuation at side zones than at a center zone.

As an alternative, forming window 1132 as a flat window with varyingattenuation as a function of the vertical angle of the curtain enablescontrol of the sensitivity of the detector, thereby providing petimmunity. Such varying attenuation may be provided by varying thethickness of the window material, such that radiation entering fromdifferent angles will traverse a corresponding different thickness ofthe window and will be attenuated to a correspondingly different extent.

Detector 1100 preferably comprises a pyroelectric sensor 1142, disposedwithin housing 1120 adjacent top panel 1140, which receives radiationfrom field-of-view 1102 via aperture 1126 and via a reflecting surface1144 which focuses the radiation onto sensor 1142.

For enhanced clarity, FIG. 23 includes an enlarged view I, whichillustrates the structure described hereinabove and an enlarged view II,which is a sectional view taken in the plane identified as II-II in viewI.

Reflecting surface 1144 is preferably defined at least partially by acollection of curves 1148 disposed along an ellipse 1150, the ellipsehaving a first focus 1152 and a second focus 1154 along a principal axisthereof, designated by reference numeral 1156. Slit axis 1128 passesthrough the second focus 1154. Each of the curves 1148 is defined by theintersection at a point 1158 on the ellipse 1150, of an imaginary slitaxis plane 1160 which includes the slit axis 1128 and an imaginaryfocusing surface 1162, such as a paraboloid or spherical surface. Thefocus of imaginary focusing surface 1162 is at the first focus 1152. Theimaginary focusing surface 1162 has an axis of symmetry 1164 which isparallel to the slit axis plane 1160. The sensor 1142 is located at thefirst focus 1152.

Due to this design of the reflecting surface 1144, radiation enteringthe aperture, which is located at the second focus 1154 of ellipse 1150,and traveling along the imaginary slit axis plane 1160 parallel to theaxis of symmetry 1164 of the imaginary focusing surface 1162, is focusedby a curve 1148 onto the sensor 1142 located at the first focus 1152 ofellipse 1150, which is also the focus of the imaginary focusing surface1162.

By varying the lengths of curves 1148, the area of the reflectingsurface 1144 which views certain portions of the field-of-view may bevaried, thus correspondingly varying the sensitivity of sensor 1142 forthose portions of the field-of-view. This variation may be useful invarious applications, such as for providing pet immunity by reducingsensitivity in regions close to the floor or for ensuring uniformity ofsensitivity along the extent of the curtain notwithstanding distancefrom the sensor.

It is appreciated that variation of the area of the reflecting surface1144 may additionally or alternatively be effected by masking selectedportions of the reflecting surface 1144.

In a preferred embodiment of the invention, such as that shown in FIG.23, pyroelectric sensor 1142 comprises a dual element pyroelectricsensor, such as an LHi-968, which is commercially available fromPerkin-Elmer of Freemont, Calif., USA.

The above described structure of detector 1100 enables the use of a verynarrow slit aperture, approximately 2-3 mm wide when using an LHi-968sensor, due to the use of reflecting surface 1144 defined as describedabove, and therefore limits interference and is mechanically robust.

It is appreciated that a reflecting surface defined as described abovewith reference to reflecting surface 1144 may be utilized as an opticalelement or as a segment forming part of an optical element in anysuitable type of detector, such as the detectors of the embodiments ofFIGS. 4, 14, 15, 21 and 22.

Reference is now made to FIG. 24, which is a simplified illustration ofa detector 1200 constructed and operative in accordance with a still afurther preferred embodiment of the present invention.

Detector 1200 preferably provides a curtain-like field-of-view,designated by reference numerals 1202. The curtain-like field-of-viewpreferably generally extends through 90 degrees from the vertical to thehorizontal as shown.

Detector 1200 preferably includes a housing 1220 and a base 1222arranged to be mounted on a vertical mounting wall 1224 such that thebase 1222 is flush with the mounting wall 1224. Housing 1220 ispreferably formed with a generally downwardly inclined slit-likeaperture, designated by reference numeral 1226, which is arranged toextend generally horizontally along a slit axis 1228 in the orientationshown in FIG. 24. The housing 1220 preferably includes a recessedhousing panel 1230 disposed below a window 1232 located at aperture1226. The recess is provided so as not to interfere with passage ofradiation into aperture 1226 in a generally vertical upward direction.Housing 1220 is preferably formed with a protruding top panel 1240disposed above window 1232.

Window 1232 preferably is made of a thin material transparent to IRradiation, such as HDPE, Silicon, Germanium or any other suitablematerial, and preferably has a circular cross-section with its centergenerally at the center of aperture 1226.

A substantial advantage of the use of a window 1232 having a circularcross section is that such a window provides generally the sameradiation attenuation at side zones and at a center zone. In contrast,were a flat window to be placed at the aperture, it would providegreater attenuation at side zones than at a center zone.

As an alternative, forming window 1232 as a flat window with varyingattenuation as a function of the vertical angle of the curtain enablescontrol of the sensitivity of the detector, thereby providing petimmunity. Such varying attenuation may be provided by varying thethickness of the window material, such that radiation entering fromdifferent angles will traverse a corresponding different thickness ofthe window and will be attenuated to a correspondingly different extent.

Detector 1200 preferably comprises a pyroelectric sensor 1242, disposedwithin housing 1220 adjacent top panel 1240, which receives radiationfrom field-of-view 1202 via aperture 1226 and via a reflecting surface1244 which focuses the radiation onto sensor 1242.

For enhanced clarity, FIG. 24 includes an enlarged view I, whichillustrates the structure described hereinabove and an enlarged view II,which is a sectional view taken in the plane identified as II-II in viewI.

Reflecting surface 1244 is preferably defined at least partially by acollection of curves, two of which are shown and respectively designatedby reference numerals 1248 and 1249. The curves are disposed along aplurality of different ellipses, two of which are shown and respectivelyindicated by reference numerals 1250 and 1251, all having a common firstfocus 1252 and a common second focus 1254 along a common principal axis1256 and all lying in the same plane. Slit axis 1228 passes through thesecond focus 1254.

Each of the curves 1248 and 1249 is defined by the intersection at apoint, here shown as points 1258 and 1259 on respective ellipses 1250and 1251 associated therewith of respective imaginary slit axis plane,here designated by reference numerals 1260 and 1261, both of whichincludes the slit axis 1228 and respective imaginary focusing surfaces,here designated by reference numerals 1262 and 1263, such as aparaboloid or spherical surface. The focus of both imaginary focusingsurfaces 1262 and 1263 is at the first common focus 1252. Each ofimaginary focusing surfaces 1262 and 1263 has an axis of symmetry, hereindicated by reference numerals 1264 and 1265, which is parallel to arespective one of slit axis planes 1260 and 1261. The sensor 1242 islocated at the first common focus 1252. Due to this design of thereflecting surface 1244, radiation entering the aperture 1226, which islocated at the second focus 1254 of the ellipses 1250 and 1251, andtraveling along the imaginary slit axis planes 1260 and 1261 parallel tothe axes of symmetry 1264 and 1265 of the imaginary focusing surfaces1262 and 1263, is focused by curves 1248 and 1249 onto the sensor 1242,located at the first focus 1252 of the ellipses 1250 and 1251, which isalso the focus of the imaginary focusing surfaces 1262 and 1263.

By varying the lengths of curves 1248 and 1249, the area of thereflecting surface 1244, which views certain portions of thefield-of-view, may be varied, thus correspondingly varying thesensitivity of sensor 1242 for those portions of the field-of-view. Thisvariation may be useful in various applications, such as for providingpet immunity by reducing sensitivity in regions close to the floor orfor ensuring uniformity of sensitivity along the extent of the curtainnotwithstanding distance from the sensor.

It is appreciated that variation of the area of the reflecting surface1244 may additionally or alternatively be effected by masking selectedportions of the reflecting surface 1244.

In a preferred embodiment of the invention, such as that shown in FIG.24, pyroelectric sensor 1242 comprises a dual element pyroelectricsensor, such as an LHi-968, which is commercially available fromPerkin-Elmer of Freemont, Calif., USA.

The above described structure of detector 1200 enables the use of a verynarrow slit aperture, approximately 2-3 mm wide when using an LHi-968sensor, due to the use of reflecting surface 1244 defined as describedabove, and therefore limits interference and is mechanically robust.Preferably, the length of the slit aperture 1226 is somewhat larger thanthe length of the longest curve defining the reflecting surface.

It is appreciated that a reflecting surface defined as described abovewith reference to reflecting surface 1244 may be utilized as an opticalelement or as a segment forming part of an optical element in anysuitable type of detector, such as the detectors of the embodimentsshown in FIGS. 4, 14, 15, 21 and 22.

Reference is now made to FIG. 25, which is a simplified illustration ofa detector 1300 constructed and operative in accordance with yet anadditional preferred embodiment of the present invention.

Detector 1300 preferably provides a curtain-like field-of-view,designated by reference numeral 1302. The curtain-like field-of-viewpreferably generally extends through 90 degrees from the vertical to thehorizontal as shown.

Detector 1300 preferably includes a housing 1320 and a base 1322arranged to be mounted on a vertical mounting wall 1324 such that thebase 1322 is flush with the mounting wall 1324. Housing 1320 ispreferably formed with a generally downwardly inclined slit-likeaperture, designated by reference numeral 1326, which is arranged toextend generally horizontally along an aperture axis 1328 in theorientation shown in FIG. 25. The housing 1320 preferably includes arecessed housing panel 1330 disposed below a window 1332 located ataperture 1326. The recess is provided so as not to interfere withpassage of radiation into aperture 1326 in a generally vertical upwarddirection. Housing 1320 is preferably formed with a protruding top panel1340 disposed above window 1332.

Window 1332 preferably is made of a thin material transparent to IRradiation, such as HDPE, Silicon, Germanium or any other suitablematerial, and preferably has a circular cross-section with its centergenerally at location 1336 at the center of aperture 1326.

Window 1332 may be formed with varying attenuation as a function of thevertical angle of the curtain, thus enabling control of the sensitivityof the detector, thereby providing pet immunity. Such varyingattenuation may be provided by varying the thickness of the windowmaterial, such that radiation entering from different angles willtraverse a corresponding different thickness of the window and will beattenuated to a correspondingly different extent.

Detector 1300 preferably comprises a pyroelectric sensor 1342, disposedwithin housing 1320, which receives radiation from field-of-view 1302via aperture 1326 and via a reflecting surface 1344 which focuses theradiation onto sensor 1342 via at least one intermediate reflectingsurface 1345.

For enhanced clarity, FIG. 25 includes an enlarged view I, whichillustrates the structure described hereinabove and an enlarged view II,which is a sectional view taken in the plane identified as II-II in viewI.

Reflecting surface 1344 is preferably defined at least partially by acollection of curves, two of which are shown and respectively designatedby reference numerals 1348 and 1349. The curves are disposed along aplurality of different ellipses, two of which are shown and respectivelyindicated by reference numerals 1350 and 1351, all having a common firstfocus 1352 and a common second focus 1354 along a common principal axis1356 and all lying in the same plane. Aperture axis 1328 passes throughthe second focus 1354.

Each of the curves 1348 and 1349 is defined by the intersection at apoint, here shown as points 1358 and 1359 on respective ellipses 1350and 1351 associated therewith, of respective imaginary aperture axisplanes, here designated by reference numerals 1360 and 1361, both ofwhich include the aperture axis 1328, and respective imaginary focusingsurfaces, here indicated by reference numerals 1362 and 1363, such as aparaboloid or spherical surface. The focus of both imaginary focusingsurfaces 1362 and 1363 is at the first common focus 1352. Each of theimaginary focusing surfaces 1362 and 1363 has an axis of symmetry, hereindicated by reference numerals 1364 and 1365, which is parallel to arespective one of aperture axis planes 1360 and 1361.

Due to this design of the reflecting surface 1344, radiation enteringthe aperture 1326, which is located at the second focus 1354 of theellipses 1350 and 1351, and traveling along the imaginary slit axisplanes 1360 and 1361 parallel to the axes of symmetry 1364 and 1365 ofthe imaginary focusing surfaces 1362 and 1363, is focused by curves 1348and 1349 onto the sensor 1342, located at the first focus 1352 of theellipses 1350 and 1351, which is also the focus of the imaginaryfocusing surfaces 1362 and 1363.

The sensor 1342 may be located at any suitable location within thehousing 1320. The at least one intermediate reflecting surface 1345,here shown as a single intermediate reflecting surface, is located alongan optical path defined by reflecting surface 1344 at a locationsuitable for redirecting radiation from reflecting surface 1344 topyroelectric sensor 1342.

In the illustrated embodiment of FIG. 25, the sensor 1342 is shownmounted at an aperture in reflecting surface 1344. It is appreciatedthat alternatively, the sensor 1342 may be located rearwardly of anaperture in the reflecting surface 1344, and in such a case may bemounted on a circuit board (not shown) which also mounts reflectingsurface 1344. In such a case, intermediate reflecting surface 1345 mayrequire some optical power.

By varying the lengths of curves 1348 and 1349, the area of thereflecting surface 1344, which views certain portions of thefield-of-view, may be varied, thus correspondingly varying thesensitivity of sensor 1342 for those portions of the field-of-view. Thisvariation may be useful in various applications, such as for providingpet immunity by reducing sensitivity in regions close to the floor, forensuring uniformity of sensitivity along the extent of the curtainnotwithstanding distance from the sensor or for compensating for theaperture formed in reflecting surface 1344.

It is appreciated that variation of the area of the reflecting surface1344 may additionally or alternatively be effected by masking selectedportions of the reflecting surface 1344.

In a preferred embodiment of the invention, such as that shown in FIG.25, pyroelectric sensor 1342 comprises a dual element pyroelectricsensor, such as an LHi-968, which is commercially available fromPerkin-Elmer of Freemont, Calif., USA.

The above described structure of detector 1300 enables the use of a verynarrow slit aperture, approximately 2-3 mm wide when using an LHi-968sensor, due to the use of reflecting surface 1344 defined as describedabove, and therefore limits interference and is mechanically robust.Preferably, the length of the slit aperture 1326 is somewhat larger thanthe length of the longest curve defining the reflecting surface.

It is appreciated that a reflecting surface defined as described abovewith reference to reflecting surface 1344 may be utilized as an opticalelement or as a segment forming part of an optical element in anysuitable type of detector, such as the detectors of the embodimentsshown in FIGS. 4, 5, 14, 15, 21 and 22.

Reference is now made to FIG. 26, which is a simplified pictorialillustration of a mirror-based detector constructed and operative inaccordance with a still additional preferred embodiment of the presentinvention. As seen in FIG. 26, the detector typically includes a mirrorhaving seven mirror segments, each defining a corresponding zone. Themirror segments are arranged in a mutually concave arrangement.

Detector 1400 preferably provides a plurality of curtain-like zones,designated by reference numerals 1402, 1404, 1406, 1408, 1410, 1412 and1414. The curtain-like zones preferably generally extend through 90degrees from the vertical to the horizontal as shown, and aredistributed azimuthally generally through 90 degrees as shown, thusproviding coverage of the entire room in which the detector isinstalled, when mounted in the corner of the room.

Detector 1400 preferably includes a housing 1420 and a base 1422arranged to be mounted at a corner of a pair of vertical walls 1424.Housing 1420 is preferably formed with an aperture 1426. The housing1420 preferably includes a recessed housing panel 1430 disposed below awindow 1432 located at aperture 1426. The recess is provided so as notto interfere with passage of radiation into aperture 1426 in a generallyvertical upward direction. Housing 1420 is preferably formed with aprotruding top panel 1440 disposed above window 1432.

Detector 1400 preferably comprises a pyroelectric sensor 1442, disposedwithin housing 1420 adjacent top panel 1440, which receives radiationfrom zones 1402-1414 via aperture 1426 and via a reflecting surface 1444which focuses the radiation onto sensor 1442.

Reflecting surface 1444 typically comprises seven mirror segments 1452,1454, 1456, 1458, 1460, 1462 and 1464, which are respectively associatedwith zones 1402, 1404, 1406, 1408, 1410, 1412 and 1414. The mirrorsegments 1452, 1454, 1456, 1458, 1460, 1462 and 1464 are arranged in aconcave arrangement preferably in a circular arc within a housingelement 1420.

Each of mirror segments 1452, 1454, 1456, 1458, 1460, 1462 and 1464 ispreferably defined at least partially by a collection of curves, similarto curves 1148 shown in FIG. 23, disposed along one or more ellipses1470, having a common first focus 1472 and a common second focus 1474along a common principal axis 1476 and lying in the same plane.

For each of the mirror segments, a respective aperture axis 1477 passesthrough the second focus 1474. Each of the curves in a mirror segment isdefined by the intersection at a point 1478 on a respective ellipse1470, of a respective imaginary aperture axis plane 1480, which includesthe aperture axis 1477, and a respective imaginary focusing surface1482, such as a paraboloid or spherical surface. The focus of eachimaginary focusing surface 1482 is at the first focus 1472.

Each imaginary focusing surface 1482 has an axis of symmetry 1484 whichis parallel to a respective aperture axis plane 1480. The sensor 1442 islocated at the first focus 1472. As a result, radiation passing throughaperture 1426 along each aperture axis plane 1480 of each curve isfocused onto the sensor at the first focus 1472 by that curve.

By varying the lengths of the curves, the area of each of the segments1452, 1454, 1456, 1458, 1460, 1462 and 1464 which views a certainportion of its respective zone may be varied, thus correspondinglyvarying the sensitivity of sensor 1442 for that portion. This variationmay be useful in various applications, such as for providing petimmunity by reducing sensitivity in regions close to the floor or forensuring uniformity of sensitivity along the extent of the curtainnotwithstanding distance from the sensor.

Window 1432 preferably is made of a thin material transparent to IRradiation, such as HDPE, Silicon, Germanium or any other suitablematerial, and preferably has a circular cross-section with its centergenerally at location 1486 at the center of aperture 1426.Alternatively, other appropriate window shapes, such as a tire-likewindow shape, may be used.

A substantial advantage of the use of a window 1432 having a tire-likeshape is that such a window provides generally the same radiationattenuation at side zones and at a center zone. In contrast, were a flatwindow or a window having a circular cross section to be placed at theaperture, it would provide greater attenuation at side zones than at acenter zone.

As an alternative, forming window 1432 with varying attenuation as afunction of the vertical angle of the curtain enables control of thesensitivity of the detector, thereby providing pet immunity. Suchvarying attenuation may be provided by varying the thickness of thewindow material, such that radiation entering from different angles willtraverse a corresponding different thickness of the window and will beattenuated to a correspondingly different extent.

In a preferred embodiment of the invention, such as that shown in FIG.26, pyroelectric sensor 1442 comprises a dual element pyroelectricsensor, such as an LHi-968, which is commercially available fromPerkin-Elmer of Freemont, Calif., USA.

It is a particular feature of the embodiment of FIG. 26 that anextremely small common aperture 1426, which is substantially narrower inboth dimensions than apertures commonly used in PIR detectors, isprovided. Preferably dimensions of the aperture are 4 mm×8 mm when usinga sensor such as LHi-968, which provides coverage of an area of 15 m×15m. It is appreciated that all of the zones defined by the mirrorsegments are positioned so that they intersect generally at one location1486 at the center of common aperture 1426. Preferably, aperture 1426 isdesigned to frame location 1486 as closely as possible withoutobstructing the zones.

The advantages of the use of an extremely small aperture housingstructure are even greater than those described hereinabove withreference to the embodiments of FIGS. 12-17, inasmuch as the aperture isnearly invisible from a distance and thus enables the detector to beeffectively hidden from view.

Reference is now made to FIG. 27, which is a simplified pictorialillustration of a detector constructed and operative in accordance witha further preferred embodiment of the present invention, to FIG. 28,which is a simplified interior view pictorial illustration of thedetector of FIG. 27, and to FIGS. 29A and 29B which are sectionalillustrations taken along respective section lines XXIXA-XXIXA andXXIXB-XXIXB in FIG. 28.

As seen in FIGS. 27-29B, there is provided a ceiling detector 1500 whichpreferably comprises four detection modules, respectively designated byreference numerals 1502, 1504, 1506 and 1508, having respectivedetection module fields-of-view, respectively designated by referencenumerals 1512, 1514, 1516 and 1518, each preferably generally viewing aquarter of a room in which the detector 1500 is placed, as shownparticularly in FIG. 27. As can be readily seen in FIGS. 27-29B, each ofthe detection module fields-of-view 1512, 1514, 1516 and 1518 includesmultiple zones which are arranged in plural layers.

Detector 1500 is operative to indicate when an intruder passes throughany of detection module fields-of-view 1512, 1514, 1516 and 1518according to predetermined criteria. A certain amount of overlap may beprovided between the detection module fields-of-view.

Detector 1500 preferably includes a housing 1520 and a base 1522arranged to be mounted on a ceiling 1524 such that the base 1522 isflush with the ceiling. It is a particular feature of the presentinvention that housing 1520 is preferably formed with four elongateapertures, respectively designated by reference numerals 1532, 1534,1536 and 1538, suitably aligned with respective detection modules 1502,1504, 1506 and 1508. A window is typically disposed adjacent each ofapertures 1532, 1534, 1536 and 1538. The windows are preferably made ofa thin material transparent to IR radiation, such as HDPE, Silicon,Germanium or any other suitable material. The windows are preferablyflat, but, alternatively, windows having a circular cross section may beused.

Detection module 1502 preferably comprises a pyroelectric sensor 1542,which receives radiation from detection module field-of-view 1512 viaelongate aperture 1532 and via a multi-segmented mirror 1546 whichfocuses the radiation onto sensor 1542 via an intermediate reflectivesurface 1548, which is preferably a hyperboloid surface.

Similarly, each of detection modules 1504, 1506 and 1508 preferablycomprises a pyroelectric sensor, which are respectively designated byreference numerals 1554, 1556 and 1558. Pyroelectric sensors 1554, 1556and 1558 respectively receive radiation from detection modulefields-of-view 1514, 1516 and 1518 via elongate apertures 1534, 1536 and1538 and via reflecting surfaces 1574, 1576 and 1578 which focus theradiation via intermediate reflective surfaces 1584, 1586 and 1588 ontosensors 1554, 1556 and 1558.

It is a particular feature of the embodiment of FIGS. 27-29B thatnarrow, slit type common apertures 1532, 1534, 1536 and 1538 areprovided. It is appreciated that all of the zones in each layer definedby the various mirror segments in a multi-segment mirror of a givendetection module, such as segments 1590, 1592, 1594 and 1596 of a layer1598 of reflective surface 1546 shown with particular clarity in FIG.29B, are positioned so that they intersect generally at one locationcentered at the aperture 1532. Preferably, the aperture is designed toframe the location as closely as possible without obstructing the zones.A relatively narrow area surrounds the location of intersection,ensuring that the housing surrounding the aperture does not obscure thezones.

The advantages of the use of a narrow aperture housing structure aredescribed hereinabove with reference to the embodiments shown in FIGS.12-17.

In a preferred embodiment of the invention, such as that shown in FIGS.27-29B, pyroelectric sensors 1542, 1554, 1556 and 1558 each comprise adual element pyroelectric sensor, such as an LHi-968, which iscommercially available from Perkin-Elmer of Freemont, Calif., USA.

A peripheral guard element (not shown) may be formed surrounding windowsformed adjacent each of apertures 1532, 1534, 1536 and 1538 to provideenhanced protection thereto. The small aperture, typically covered by asmall window, additionally may serve as a radiation filter, allowingonly radiation of a certain wavelength range, such as IR radiation, topass therethrough. The relatively narrow, small sized window reduces thecost of the filter. Furthermore, it is easier to apply anti-maskingmeasures to protect a narrow window, than to protect a wide window.

Reference is now made to FIG. 30, which is a simplified pictorialillustration of a detector constructed and operative in accordance witha further preferred embodiment of the present invention, to FIG. 31,which is a simplified interior view pictorial illustration of thedetector of FIG. 30, and to FIGS. 32A and 32B which are sectionalillustrations taken along respective section lines XXXIIA-XXXIIA andXXXIIB-XXXIIB in FIG. 31.

As seen in FIGS. 30-32B, there is provided a ceiling detector 1600 whichpreferably comprises four multi-segment reflectors, respectivelydesignated by reference numerals 1602, 1604, 1606 and 1608, havingrespective reflector view regions, respectively designated by referencenumerals 1612, 1614, 1616 and 1618, each preferably generally viewing aquarter of a room in which the detector 1600 is placed, as shownparticularly in FIG. 30. As can be readily seen in FIG. 30, each of thereflector view regions 1612, 1614, 1616 and 1618 includes multiple zoneswhich are arranged in plural layers.

Detector 1600 is operative to indicate when an intruder passes throughany of reflector view regions 1612, 1614, 1616 and 1618 according topredetermined criteria. A certain amount of overlap may be providedbetween the reflector view regions.

Detector 1600 preferably includes a housing 1620 and a base 1622arranged to be mounted on a ceiling 1624 such that the base 1622 isflush with the ceiling. It is a particular feature of the presentinvention that housing 1620 is preferably formed with four elongateapertures, respectively designated by reference numerals 1632, 1634,1636 and 1638, suitably aligned with respective multi-segment reflectors1602, 1604, 1606 and 1608. A window is typically disposed adjacent eachof apertures 1632, 1634, 1636 and 1638. The windows are preferably madeof a thin material transparent to IR radiation, such as HDPE, Silicon,Germanium or any other suitable material. The windows are preferablyflat windows, but, alternatively, windows having a circular crosssection may be used.

Detector 1600 preferably comprises a single pyroelectric sensor 1640which receives radiation from reflector view regions 1612, 1614, 1616and 1618 via elongate apertures 1632, 1634, 1636 and 1638 andmulti-segment reflectors 1602, 1604, 1606 and 1608 which focus theradiation onto sensor 1640 via at least one intermediate reflectivesurface 1650, which is preferably a hyperboloid surface.

It is a particular feature of the embodiment of FIGS. 30-32B thatnarrow, slit type common apertures 1632, 1634, 1636 and 1638 areprovided. It is appreciated that all of the zones in each zone layerdefined by the various mirror segments in each multi-segment mirror,such as segments 1690, 1692, 1694 and 1696 of a layer 1698 of reflectivesurface 1602 shown with particular clarity in FIG. 32, are positioned sothat they intersect generally at one location centered at the aperture.Preferably, the aperture is designed to frame the location as closely aspossible without obstructing the zones. A relatively narrow areasurrounds the location of intersection, ensuring that the housingsurrounding the aperture does not obscure the zones.

The advantages of the use of a narrow aperture housing structure aredescribed hereinabove with reference to the embodiments shown in FIGS.12-17.

In a preferred embodiment of the invention, such as that shown in FIGS.30-32B, pyroelectric sensor 1640 comprises a dual element pyroelectricsensor, such as an LHi-968, which is commercially available fromPerkin-Elmer of Freemont, Calif., USA.

In an alternative embodiment, one of the two sensing elements inpyroelectric dual-element sensor 1640 is covered. In this arrangement,pyroelectric sensor 1640 employs a single pyroelectric sensing elementand may employ the covered sensing element for thermal compensation asis known in the art.

As another alternative, instead of using a dual element pyroelectricsensor and covering one element, a single element pyroelectric sensormay be used, such as SSAC10-11, commercially available from NipponCeramics Co. of Japan. Any other sensors suitable for ceiling mountdetectors can be used.

A peripheral guard element (not shown) may be formed surrounding windowsformed adjacent each of apertures 1632, 1634, 1636 and 1638 to provideenhanced protection thereto. The small aperture, typically covered by asmall window, additionally may serve as a radiation filter, allowingonly radiation of a certain wavelength range, such as IR radiation, topass therethrough. The relatively narrow, small sized window reduces thecost of the filter. Furthermore, it is easier to apply anti-maskingmeasures to protect a narrow window, than to protect a wide window.

Reference is now made to FIG. 33, which is a simplified sectionalillustration of a detector constructed and operative in accordance witha still further preferred embodiment of the present invention.

As seen in FIG. 33, there is provided a ceiling corner detector 1700which preferably comprises a single multi-segment reflector 1702 havinga field-of-view region 1706 viewing an entire room in which the detector1700 is placed. As can be readily seen in FIG. 33, the field-of-viewregion 1706 includes multiple zones which are arranged in plural layers.

Detector 1700 is operative to indicate when an intruder passes throughfield-of-view 1706 according to predetermined criteria.

Detector 1700 preferably includes a housing 1710 and a base 1712arranged to be mounted at the corner 1714 of a ceiling such that thebase 1712 is flush with the ceiling. It is a particular feature of thepresent invention that housing 1710 is preferably formed with anelongate aperture 1722, suitably aligned with multi-segment reflector1702.

Detector 1700 preferably comprises a single pyroelectric sensor 1724,which receives radiation from the field-of-view region 1706 via elongateaperture 1722 and multi-segment reflector 1702 which focuses theradiation onto sensor 1724 via an intermediate reflective surface 1728,which is preferably a hyperboloid surface.

It is a particular feature of the embodiment of FIG. 33 that commonelongate aperture 1722 is provided. It is appreciated that all of thezones in each zone layer defined by the various mirror segments inmulti-segment reflective surface such as segments 1730, 1732, 1734 and1736 of layer 1738, shown with particular clarity in view II of FIG. 33,are positioned so that they intersect generally at one location centeredat the aperture. Preferably, the aperture is designed to frame thelocation as closely as possible without obstructing the zones. Arelatively narrow area surrounds the location of intersection, ensuringthat the housing surrounding the aperture does not obscure the zones.

The advantages of the use of a narrow aperture housing structure aredescribed hereinabove with reference to the embodiments shown in FIGS.12-17.

In a preferred embodiment of the invention, such as that shown in FIG.33, the pyroelectric sensors 1724 comprises a dual element pyroelectricsensor, such as an LHi-968, which is commercially available fromPerkin-Elmer of Freemont, Calif., USA.

Reference is now made to FIG. 34, which is a pictorial illustration of adetector assembly constructed in accordance with yet another preferredembodiment of the present invention, to FIGS. 35A and 35B, which arerespective sectional illustrations thereof, to FIGS. 36A and 36B, whichare respectively, a top view illustration and a side view illustrationof a radiation pattern received by the detector assembly of FIG. 34, andto FIG. 37, which is a block diagram of the detector assembly of FIG.34.

Specifically, FIG. 34 is a general view of a detector assembly 1800comprising two detectors 1810 and 1812 in a single housing element 1814,each detector including a pyroelectric sensor associated with one ormore corresponding lens segment, defining a corresponding detectionregion, including a plurality of detection zones. The zones of each ofthe two detection regions are not overlapping.

As seen in FIGS. 34 to 37, the detectors are arranged so that each ofdetectors 1810 and 1812 is exclusively associated with different lenssegments.

In the illustrated embodiment, a sensor 1816 of detector 1810 isassociated with five pairs of lens segments, each pair defining twovertically distributed detection zones, indicated by reference numerals1817 and 1818 which are shown with particular clarity in FIG. 36B.Preferably, vertical detection zone 1817 is a beam-shaped detection zoneand vertical detection zone 1818 is a curtain-like detection zone. Thezones defined by the pairs of lens segments are azimuthally distributed.Lens segments 1820 and 1822 define a pair of detection zones 1823. In asimilar manner, lens segments 1824 and 1826 define a pair of detectionzones 1827, lens segments 1828 and 1830 define a pair of detection zones1831, lens segments 1832 and 1834 define a pair of detection zones 1835and lens segments 1836 and 1838 define a pair of detection zones 1839.

As shown in FIG. 34, the lens segments 1820 and 1822, 1824 and 1826,1828 and 1830, 1832 and 1834 and 1836 and 1838 are preferably arrangedin a convex arrangement along a circular arc, in two rows. The lenssegments 1820, 1824, 1828, 1832 and 1836 are preferably Fresnel lenses,while the lens segments 1822, 1826, 1830, 1834 and 1838 are preferablycylindrical type lenses. Any other suitable type of lens elements, suchas, for example, diffractive lenses, and any suitable arrangementthereof, may be employed.

A sensor 1846, forming part of detector 1812, is associated with fourpairs of lens segments, each pair defining two vertically distributeddetection zones, similar to detection zones 1817 and 1818 (FIG. 36B).The zones defined by the pairs of lens segments are azimuthallydistributed. Lens segments 1850 and 1852 define a pair of detectionzones 1853. In a similar manner lens segments 1854 and 1856 define apair of detection zones 1857, lens segments 1858 and 1860 define a pairof detection zones 1861 and lens segments 1862 and 1864 define a pair ofdetection zones 1865.

As shown in FIG. 34, the lens segments 1850 and 1852, 1854 and 1856,1858 and 1860 and 1862 and 1864 are preferably arranged in a convexarrangement along a circular arc, in two rows. The lens segments 1850,1854, 1858 and 1862 are preferably Fresnel lenses, while the lenssegments 1852, 1856, 1860 and 1864 are preferably cylindrical typelenses. Any other suitable type of lens elements, such as, for example,diffractive lenses, and any suitable arrangement thereof, may beemployed.

It is a particular feature of the present invention that the opticalcenters of lens segments 1850 and 1852 are located azimuthally betweenthe optical centers of lens segments 1820 and 1824, as indicated by adashed line in FIG. 34. In a similar manner, the optical centers of lenssegments 1854 and 1856 are located azimuthally between the opticalcenters of lens segments 1824 and 1828, the optical centers of lenssegments 1858 and 1860 are located azimuthally between the opticalcenters of lens segments 1828 and 1832 and the optical centers of lenssegments 1862 and 1864 are located azimuthally between the opticalcenters of lens segments 1832 and 1836. As shown with particular clarityin FIGS. 34, 35A and 35B, the optical axes of detection zones 1823,1827, 1831, 1835 and 1839, shown in FIG. 35A, are interlaced with theoptical axes of detection zones 1853, 1857, 1861 and 1865, shown in FIG.35B.

As seen with particular clarity in FIG. 36A, each of the detectors 1810and 1812 has a plurality of azimuthally distributed detection zones. Inaccordance with a preferred embodiment of the present invention, theazimuthally distributed detection zones 1823, 1827, 1831, 1835 and 1839of detector 1810 are non-overlapping with the azimuthally distributeddetection zones 1853, 1857, 1861 and 1865 of detector 1812.Additionally, the detection zones 1823, 1827, 1831, 1835 and 1839 ofdetector 1810 are azimuthally interlaced with detection zones 1853,1857, 1861 and 1865 of detector 1812 in a pattern such that interferenceconfined to one detection zone of one of detectors 1810 and 1812 is notsensed by an adjacent detection zone of the other of detectors 1810 and1812.

It is appreciated that detector assembly 1800 may be formed with anysuitable detection zone pattern having interlaced detection zones whichdo not overlap. For example, each of the detection zones of detectors1810 and 1812 may include four detection zone fingers, or any othersuitable number of detection zone fingers.

As seen with particular clarity in FIGS. 36A and 36B, it is a particularfeature of the present invention that the detectors 1810 and 1812provide coverage over generally the same azimuthal detection region.

As seen with particular clarity in FIG. 36A, it is a particular featureof the present invention that some individual detection zones ofdetector 1810 are each located intermediate a pair of individualdetection zones of detector 1812, and individual detection zones ofdetector 1812 are each located intermediate a pair of individualdetection zones of detector 1810. The detection zones of detectors 1810and 1812 are interlaced at least at a central portion of the azimuthaldetection region.

Each of the detectors 1810 and 1812 comprises independent signalprocessing circuitry 1872 and 1874 which provides a separate independentdetector output to an external alarm control panel 1870, preferably byseparate output relays 1876 and 1878, and separate connecting wires 1880and 1882 respectively. Output relays 1876 and 1878 may be wired, or mayalternatively be wireless output transmitters.

The detectors 1810 and 1812 may provide detection output signalsseparately to alarm control panel 1870.

Reference is now made to FIG. 38, which is a pictorial illustration of adetector assembly constructed in accordance with still another preferredembodiment of the present invention, to FIGS. 39A and 39B, which arerespectively, a top view illustration and a side view illustration of aradiation pattern received by the detector assembly of FIG. 38, and toFIG. 40, which is a block diagram of the detector assembly of FIG. 38.

Specifically, FIG. 38 is a general view of a detector assembly 1900comprising two detectors 1910 and 1912 in a single housing element 1914,each detector including a pyroelectric sensor associated withcorresponding mirror segment, defining a corresponding detection region,including a plurality of detection zones. The zones of each of the twodetection regions are not overlapping.

As seen in FIGS. 38 to 40, the detectors are arranged so that each ofdetectors 1910 and 1912 is exclusively associated with different mirrorsegments.

In the illustrated embodiment, a sensor 1916 of detector 1910 isassociated with five pairs of mirror segments, one of which is indicatedby reference numerals 1917 and 1918 in Section A-A of FIG. 38, each pairdefining two vertically distributed detection zones, indicated byreference numerals 1919 and 1920 which are shown with particular clarityin FIG. 39B. The zones defined by the pairs of mirror segments areazimuthally distributed as shown in FIG. 39A. The five pairs of mirrorsegments, indicated by reference numerals 1917, 1922, 1924, 1926 and1928 define respective detection zones indicated by reference numerals1930, 1932, 1934, 1936 and 1938.

As shown in FIG. 38, the housing element 1914 defines a top relativelynarrow slit aperture 1940 adjacent which is preferably located a window1942, preferably having a circular cross-section with its centergenerally at a location 1944 at the center of aperture 1940. Window 1942preferably is made of a thin material transparent to IR radiation, suchas HDPE, Silicon, Germanium or any other suitable material.Alternatively, other appropriate window shapes may be used.

A substantial advantage of the use of a window 1942 having a circularcross section is that such a window provides generally the sameradiation attenuation at side zones and at a center zone. In contrast,were a flat window to be placed at the aperture, it would providegreater attenuation at side zones than at a center zone.

A sensor 1946, forming part of detector 1912, is associated with fourpairs of mirror segments, each pair defining two vertically distributeddetection zones, similar to detection zones 1917 and 1918 (FIG. 39B).The zones defined by the pairs of mirror segments are azimuthallydistributed. The four pairs of mirror segments, indicated by referencenumerals 1950, 1952, 1954 and 1956 define respective detection zonesindicated by reference numerals 1960, 1962, 1964 and 1966.

As shown in FIG. 38, the housing element 1914 defines a bottomrelatively narrow slit aperture 1970 adjacent which is preferablylocated a common window 1972, preferably having a circular cross-sectionwith its center generally at a location 1974 at the center of aperture1970. Window 1972 preferably is made of a thin material transparent toIR radiation, such as HDPE, Silicon, Germanium or any other suitablematerial. Alternatively, other appropriate window shapes may be used.

A substantial advantage of the use of a window 1972 having a circularcross section is that such a window provides generally the sameradiation attenuation at side zones and at a center zone. In contrast,were a flat window to be placed at the aperture, it would providegreater attenuation at side zones than at a center zone.

It is a particular feature of the embodiment of FIGS. 38 to 40 thatnarrow, slit type apertures 1940 and 1970 are provided. It isappreciated that all of the zones defined by each single horizontallayer of the mirror segments of detector 1910 are positioned so thatthey intersect generally at one location centered at location 1944.Preferably, aperture 1940 is designed to frame location 1944 as closelyas possible without obstructing the zones. A relatively narrow areasurrounds location 1944, just large enough to ensure that the housingsurrounding aperture 1940 does not obscure the zones. In a similarmanner, all of the zones defined by each single horizontal layer of themirror segments of detector 1912 are positioned so that they intersectgenerally at one location centered at location 1974. Preferably,aperture 1970 is designed to frame location 1974 as closely as possiblewithout obstructing the zones. A relatively narrow area surroundslocation 1974, just large enough to ensure that the housing surroundingaperture 1970 does not obscure the zones.

The advantages of the use of a narrow aperture housing structure aredescribed hereinabove with reference to the embodiments of FIGS. 12-17.

Sensors 1916 and 1946 preferably comprise dual element pyroelectricsensors such as LHi-968 sensors, commercially available fromPerkin-Elmer of Freemont, Calif., USA.

As seen with particular clarity in FIG. 39A, each of the detectors 1910and 1912 has a plurality of azimuthally distributed detection zones. Inaccordance with a preferred embodiment of the present invention, theazimuthally distributed detection zones 1930, 1932, 1934, 1936 and 1938of detector 1910 are non-overlapping with the azimuthally distributeddetection zones 1960, 1962, 1964 and 1966 of detector 1912.Additionally, the detection zones 1930, 1932, 1934, 1936 and 1938 ofdetector 1910 are azimuthally interlaced with detection zones 1960,1962, 1964 and 1966 of detector 1912 in a pattern such that interferenceconfined to one detection zone of one of detectors 1910 and 1912 is notsensed by an adjacent detection zone of the other of detectors 1910 and1912.

It is appreciated that detector assembly 1900 may be formed with anysuitable detection zone pattern having interlaced detection zones whichdo not overlap. For example, each of the detection zones of detectors1910 and 1912 may include four detection zone fingers, or any othersuitable number of detection zone fingers.

As seen with particular clarity in FIGS. 39A and 39B, it is a particularfeature of the present invention that the detectors 1910 and 1912provide coverage over generally the same azimuthal detection region.

As seen with particular clarity in FIG. 39A, it is a particular featureof the present invention that some individual detection zones ofdetector 1910 are each located intermediate a pair of individualdetection zones of detector 1912, and individual detection zones ofdetector 1912 are each located intermediate a pair of individualdetection zones of detector 1910. The detection zones of detectors 1910and 1912 are interlaced at least at a central portion of the azimuthaldetection region.

Each of the detectors 1910 and 1912 provides a separate detector outputto an external alarm control panel 1980, preferably by processingdetections using separate signal processing assemblies 1982 and 1984 andproviding output via separate output relays 1986 and 1988 and separateconnecting wires 1990 and 1992, respectively. Output relays 1986 and1988 may be wired, or may alternatively be wireless output transmitters.

The detectors 1910 and 1912 may provide detection output signalsseparately to alarm control panel 1980.

Reference is now made to FIG. 41, which is a pictorial illustration of adetector assembly 2000 constructed in accordance with a furtherpreferred embodiment of the present invention, to FIGS. 42A and 42B,which are respectively, a top view illustration and a side viewillustration of a radiation pattern received by the detector assembly ofFIG. 41, and to FIG. 43, which is a block diagram of the detectorassembly of FIG. 41.

Specifically, FIG. 41 is a general view of a detector assembly 2000comprising two detectors 2010 and 2012 in a single housing element 2014,each detector including a pyroelectric sensor associated with acorresponding mirror segment, defining a corresponding detection region,including a plurality of curtain-like detection zones. The zones of eachof the two detection regions are not overlapping. The mirror segments ofeach of detectors 2010 and 2012 are arranged in a mutually concavearrangement. The curtain-like detection zones preferably generallyextend through 90 degrees from the vertical to the horizontal anddiverge generally through 90 degrees.

As seen in FIGS. 41 to 43, the detectors are arranged so that each ofdetectors 2010 and 2012 is exclusively associated with different mirrorsegments.

In the illustrated embodiment, a sensor 2016 of detector 2010 isassociated with five mirror segments, each defining a single verticallydistributed curtain-like detection zone indicated by reference numeral2018 which is shown with particular clarity in FIG. 42B. The zonesdefined by the mirror segments are azimuthally distributed. The fivepairs of mirror segments, indicated by reference numerals 2020, 2022,2024, 2026 and 2028, define respective detection zones indicated byreference numerals 2030, 2032, 2034, 2036 and 2038.

As shown in FIG. 41, the housing element 2014 preferably defines a toprelatively narrow slit aperture 2040 adjacent which is preferablylocated a window 2041, preferably having a circular cross-section withits center generally at a location 2042 at the center of aperture 2040.The housing element 2014 preferably includes a top recessed housingpanel 2043 disposed below window 2041 located at aperture 2040. Therecess is provided so as not to interfere with passage of radiation intoaperture 2040 in a generally vertical upward direction. Housing 2014 ispreferably formed with a protruding top panel 2044 disposed above window2041, adjacent which is disposed sensor 2016. Window 2041 preferably ismade of a thin material transparent to IR radiation, such as HDPE,Silicon, Germanium or any other suitable material. Alternatively, otherappropriate window shapes, such as a tire-like window shape, may beused.

A substantial advantage of the use of a window 2041 having a tire-likeshape is that such a window provides generally the same radiationattenuation at side zones and at a center zone. In contrast, were a flatwindow or a window having a circular cross section to be placed at theaperture, it would provide greater attenuation at side zones than at acenter zone.

A sensor 2046, forming part of detector 2012, is associated with fourpairs of mirror segments, each defining a single vertically distributedcurtain-like detection zone, similar to detection zone 2018 (FIG. 42B).The zones defined by the mirror segments are azimuthally distributed.The four mirror segments, indicated by reference numerals 2050, 2052,2054 and 2056 define respective detection zones indicated by referencenumerals 2060, 2062, 2064 and 2066.

As shown in FIG. 41, the housing element 2014 preferably defines abottom relatively narrow slit aperture 2070 adjacent which is preferablylocated a window 2071, preferably having a circular cross-section withits center generally at a location 2072 at the center of aperture 2070.The housing element 2014 preferably includes a bottom recessed housingpanel 2073 disposed below window 2071 located at aperture 2070. Therecess is provided so as not to interfere with passage of radiation intoaperture 2070 in a generally vertical upward direction. Housing 2014 ispreferably formed with a protruding bottom panel 2074 disposed abovewindow 2071, which generally protrudes to the extent of recessed panel2043, in which is disposed sensor 2046. Window 2071 preferably is madeof a thin material transparent to IR radiation, such as HDPE, Silicon,Germanium or any other suitable material. Alternatively, otherappropriate window shapes, such as a tire-like window shape, may beused.

A substantial advantage of the use of a window 2071 having a tire-likeshape is that such a window provides generally the same radiationattenuation at side zones and at a center zone. In contrast, were a flatwindow or a window having a circular cross section to be placed at theaperture, it would provide greater attenuation at side zones than at acenter zone.

It is a particular feature of the embodiment of FIGS. 41 to 43 thatnarrow, slit type common apertures 2040 and 2070 are provided. It isappreciated that all of the zones defined by the mirror segments ofdetector 2010 are positioned so that they intersect generally at onelocation centered at location 2042. Preferably, aperture 2040 isdesigned to frame location 2042 as closely as possible withoutobstructing the zones. A relatively narrow area surrounds location 2042,just large enough to ensure that the housing surrounding aperture 2040does not obscure the zones. In a similar manner, all of the zonesdefined by the mirror segments of detector 2012 are positioned so thatthey intersect generally at one location centered at location 2072.Preferably, aperture 2070 is designed to frame location 2072 as closelyas possible without obstructing the zones. A relatively narrow areasurrounds location 2072, just large enough to ensure that the housingsurrounding aperture 2070 does not obscure the zones.

The advantages of the use of an extremely small aperture housingstructure are even greater than those described hereinabove withreference to the embodiments of FIGS. 12-17 and 23-26, inasmuch as theaperture is nearly invisible from a distance and thus enables thedetector to be effectively hidden from view.

Sensors 2016 and 2046 preferably comprise dual element pyroelectricsensors such as LHi-968 sensors, commercially available fromPerkin-Elmer of Freemont, Calif., USA.

As seen with particular clarity in FIG. 42A, each of the detectors 2010and 2012 has a plurality of azimuthally distributed detection zones. Inaccordance with a preferred embodiment of the present invention, theazimuthally distributed detection zones 2030, 2032, 2034, 2036 and 2038of detector 2010 are non-overlapping with the azimuthally distributeddetection zones 2060, 2062, 2064 and 2066 of detector 2012.Additionally, the detection zones 2030, 2032, 2034, 2036 and 2038 ofdetector 2010 are azimuthally interlaced with detection zones 2060,2062, 2064 and 2066 of detector 2012 in a pattern such that interferenceconfined to one detection zone of one of detectors 2010 and 2012 is notsensed by an adjacent detection zone of the other of detectors 2010 and2012.

It is appreciated that detector assembly 2000 may be formed with anysuitable detection zone pattern having interlaced detection zones whichdo not overlap. For example, each of the detection zones of detectors2010 and 2012 may include four detection zone fingers, or any othersuitable number of detection zone fingers.

As seen with particular clarity in FIGS. 42A and 42B, it is a particularfeature of the present invention that the detectors 2010 and 2012provide coverage over generally the same azimuthal detection region.

As seen with particular clarity in FIG. 42A, it is a particular featureof the present invention that some individual detection zones ofdetector 2010 are each located intermediate a pair of individualdetection zones of detector 2012, and individual detection zones ofdetector 2012 are each located intermediate a pair of individualdetection zones of detector 2010. The detection zones of detectors 2010and 2012 are interlaced at least at a central portion of the azimuthaldetection region.

Each of the detectors 2010 and 2012 provides a separate detector outputto an external alarm control panel 2080, preferably by processingdetections using separate signal processing assemblies 2082 and 2084 andproviding output via separate output relays 2086 and 2088 and separateconnecting wires 2090 and 2092, respectively. Output relays 2086 and2088 may be wired, or may alternatively be wireless output transmitters.

The detectors 2010 and 2012 may provide detection output signalsseparately to alarm control panel 2080.

Reference is now made to FIG. 44, which is a pictorial illustration of adetector assembly constructed in accordance with still another preferredembodiment of the present invention, to FIGS. 45A and 45B, which arerespective sectional illustrations thereof, to FIGS. 46A and 46B, whichare respectively, a top view illustration and a side view illustrationof a radiation pattern received by the detector assembly of FIG. 44, andto FIG. 47, which is a block diagram of the detector assembly of FIG.44.

Specifically, FIG. 44 is a general view of a detector assembly 2100comprising two detectors 2110 and 2112 in a single housing element 2114,each detector including a pyroelectric sensor associated with one ormore corresponding lens segment, defining a corresponding detectionregion, including a plurality of detection zones. The zones of each ofthe two detection regions are not overlapping.

As seen in FIGS. 44 to 47, the detectors are arranged so that each ofdetectors 2110 and 2112 is exclusively associated with different lenssegments.

In the illustrated embodiment, a sensor 2116 of detector 2110 isassociated with five pairs of lens segments, each pair defining twovertically distributed detection zones, indicated by reference numerals2117 and 2118 which are shown with particular clarity in FIG. 46B.Preferably, vertical detection zone 2117 is a beam-shaped detection zoneand vertical detection zone 2118 is a curtain-like detection zone. Thezones defined by the pairs of lens segments are azimuthally distributed.Lens segments 2120 and 2122 define a pair of detection zones 2123. In asimilar manner, lens segments 2124 and 2126 define a pair of detectionzones 2127, lens segments 2128 and 2130 define a pair of detection zones2131, lens segments 2132 and 2134 define a pair of detection zones 2135and lens segments 2136 and 2138 define a pair of detection zones 2139.

As shown in FIG. 44, the lens segments 2120 and 2122, 2124 and 2126,2128 and 2130, 2132 and 2134 and 2136 and 2138 are preferably arrangedin a convex arrangement along a circular arc, in two rows. The lenssegments 2120, 2124, 2128, 2132 and 2136 are preferably Fresnel lenses,while the lens segments 2122, 2126, 2130, 2134 and 2138 are preferablycylindrical type lenses. Any other suitable type of lens elements, suchas, for example, diffractive lenses, and any suitable arrangementthereof, may be employed.

A sensor 2146, forming part of detector 2112, is associated with fourpairs of lens segments, each pair defining two vertically distributeddetection zones, similar to detection zones 2117 and 2118 (FIG. 46B).The zones defined by the pairs of lens segments are azimuthallydistributed. Lens segments 2150 and 2152 define a pair of detectionzones 2153. In a similar manner lens segments 2154 and 2156 define apair of detection zones 2157, lens segments 2158 and 2160 define a pairof detection zones 2161 and lens segments 2162 and 2164 define a pair ofdetection zones 2165.

As shown in FIG. 44, the lens segments 2150 and 2152, 2154 and 2156,2158 and 2160 and 2162 and 2164 are preferably arranged in a convexarrangement along a circular arc, in two rows. The lens segments 2150,2154, 2158 and 2162 are preferably Fresnel lenses, while the lenssegments 2152, 2156, 2160 and 2164 are preferably cylindrical typelenses. Any other suitable type of lens elements, such as, for example,diffractive lenses, and any suitable arrangement thereof, may beemployed.

It is a particular feature of the present invention that the opticalcenters of lens segments 2150 and 2152 are located azimuthally betweenthe optical centers of lens segments 2120 and 2124, as indicated by adashed line in FIG. 44. In a similar manner, the optical centers of lenssegments 2154 and 2156 are located azimuthally between the opticalcenters of lens segments 2124 and 2128, the optical centers of lenssegments 2158 and 2160 are located azimuthally between the opticalcenters of lens segments 2128 and 2132 and the optical centers of lenssegments 2162 and 2164 are located azimuthally between the opticalcenters of lens segments 2132 and 2136. As shown with particular clarityin FIGS. 44, 45A and 45B, the optical axes of detection zones 2123,2127, 2131, 2135 and 2139, shown in FIG. 45A, are interlaced with theoptical axes of detection zones 2153, 2157, 2161 and 2165, shown in FIG.45B.

As seen with particular clarity in FIG. 46A, each of the detectors 2110and 2112 has a plurality of azimuthally distributed detection zones. Inaccordance with a preferred embodiment of the present invention, theazimuthally distributed detection zones 2123, 2127, 2131, 2135 and 2139of detector 2110 are non-overlapping with the azimuthally distributeddetection zones 2153, 2157, 2161 and 2165 of detector 2112.Additionally, the detection zones 2123, 2127, 2131, 2135 and 2139 ofdetector 2110 are azimuthally interlaced with detection zones 2153,2157, 2161 and 2165 of detector 2112 in a pattern such that interferenceconfined to one detection zone of one of detectors 2110 and 2112 is notsensed by an adjacent detection zone of the other of detectors 2110 and2112.

It is appreciated that detector assembly 2100 may be formed with anysuitable detection zone pattern having interlaced detection zones whichdo not overlap. For example, each of the detection zones of detectors2110 and 2112 may include four detection zone fingers, or any othersuitable number of detection zone fingers.

As seen with particular clarity in FIGS. 46A and 46B, it is a particularfeature of the present invention that the detectors 2110 and 2112provide coverage over generally the same azimuthal detection region.

As seen with particular clarity in FIG. 46A, it is a particular featureof the present invention that some individual detection zones ofdetector 2110 are each located intermediate a pair of individualdetection zones of detector 2112, and individual detection zones ofdetector 2112 are each located intermediate a pair of individualdetection zones of detector 2110. The detection zones of detectors 2110and 2112 are interlaced at least at a central portion of the azimuthaldetection region.

Each of the detectors 2110 and 2112 comprises signal processingcircuitry 2172 and 2174 which provides a detector output to an externalalarm control panel 2170, preferably by separate output relays 2176 and2178, and separate connecting wires 2180 and 2182 respectively. Outputrelays 2176 and 2178 may be wired, or may alternatively be wirelessoutput transmitters. The signal processing circuitry 2172 may beinterconnected with the signal processing circuitry 2174, as indicatedby a connection 2184.

Various alternative logic algorithms may be utilized by detectors 2110and 2112 in determining when respective alarm outputs should be providedby output relays 2176 and 2178.

The detectors 2110 and 2112 may provide detection output signalsseparately to alarm control panel 2170.

In accordance with one embodiment of the present invention, each of thedetectors 2110 and 2112 may separately provide detection output signalsto alarm control panel 2170 only if the other of detectors 2110 and 2112also senses motion within a predetermined time period. This logic helpsprevent false alarms, as an alarm is not activated if the detection islimited to a single detector.

Alternatively or additionally, an alarm output may not be provided fromone of detectors 2110 and 2112 to alarm control panel 2170 if adetection output signal is generated by the other of detectors 2110 and2112 simultaneously, as simultaneous detection output signals generatedsimultaneously by both detectors 2110 and 2112 may indicate that thesignals are generated due to interference occurring in the detectionregions of both detectors and not due to motion of an intruder withinthe detection regions.

As a further alternative a multiple mode detector may be provided inwhich a user can select a mode in which detectors 2110 and 2112 mayprovide a common detection output signal to alarm control panel 2170.For example, if one of detectors 2110 and 2112 generates a motiondetection signal, and within a predetermined time duration a motiondetection signal is generated by the other of detectors 2110 and 2112,an alarm signal is initiated by the first of detectors 2110 and 2112 togenerate a motion detection signal, and a confirmed common detectionoutput signal may be provided to alarm control panel 2170 by a commonoutput relay 2186 or by either of output relays 2176 and 2178.

Preferably, one or more conditions for initiation of an alarm signal tothe control panel 2170 may be preset by the user, such as by setting oneor more switches (not shown) within detector assembly 2100 to a desiredalarm logic option.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove as well as modifications and variations thereof aswould occur to a person of skill in the art upon reading the foregoingspecification and which are not in the prior art.

1. A passive infra-red detector comprising: at least threesub-detectors, each of said at least three sub-detectors being operativeto receive infra-red radiation from a corresponding one of at leastthree sub fields-of-view, each of said at least three sub fields-of-viewbeing exclusively defined by an optical element which does not defineany other of said at least three sub fields of view, said at least threesub fields-of-view being angled with respect to each other; and reducedfalse alarm signal processing circuitry, receiving output signals fromsaid at least three sub-detectors, noting at least one of time durationsof said output signals of at least two adjacent ones of said at leastthree sub-detectors and time differences between receipt of said outputsignals from said at least two adjacent ones of said at least threesub-detectors, and providing a motion detection output, said reducedfalse alarm signal processing circuitry being operative to eliminate atleast some false alarms at least based on at least one sensed timerelationship among at least two of said at least one of time durationsof said output signals and said time differences between receipt of saidoutput signals.
 2. A passive infra-red detector according to claim 1 andwherein said at least three sub fields-of-view are substantiallynon-overlapping.
 3. A passive infra-red detector according to claim 1and wherein said signal processing circuitry is operative to processsaid output signals by noting time durations of said output signals fromadjacent ones of said at least three sub-detectors and providing saidmotion detection output at least when the ratio between said timedurations is within a predetermined range of values.
 4. A passiveinfra-red detector according to claim 3 and wherein said predeterminedrange of values is 0.5 to 2.0.
 5. A passive infra-red detector accordingto claim 1 and wherein said signal processing circuitry is operative toprocess said output signals by noting a time difference between receiptof said output signals and time durations of said output signals and toprovide said motion detection output if, in response to receipt of saidoutput signals from at least two adjacent ones of said at least threesub-detectors having respective time durations and a time differencetherebetween, said time durations and said time difference therebetweenhaving a time relationship therebetween which meets at least onepredetermined criterion.
 6. A passive infra-red detector according toclaim 5 and wherein said at least one predetermined criterion compriseswhether a ratio between said time difference and at least one of saidtime durations lies within a predetermined range of values.
 7. A passiveinfra-red detector according to claim 6 and wherein said predeterminedrange of values is based at least in part on divergence angles of atleast two zones of two different ones of said at least three subfields-of-view corresponding to said at least two adjacent ones of saidat least three sub-detectors.
 8. A passive infra-red detector accordingto claim 6 and wherein said predetermined range of values is based atleast in part on an angle between at least two zones of two differentones of said at least three sub fields-of-view corresponding to said atleast two adjacent ones of said at least three sub-detectors.
 9. Apassive infra-red detector according to claim 5 and wherein said atleast one predetermined criterion comprises whether ratios between saidtime difference and each of said time durations lie within apredetermined range of values.
 10. A passive infra-red detectoraccording to claim 1 and wherein each said optical element is directedin a corresponding direction, the corresponding directions of saidoptical elements of each two of said at least three sub-detectors beingdifferent.
 11. A passive infra-red detector according to claim 1 andwherein said optical element comprises a non focusing optical element.12. A passive infra-red detector according to claim 11 and wherein saidnon-focusing optical element comprises a reflective optical element. 13.A passive infra-red detector according to claim 1 and wherein saidoptical element comprises a focusing element.
 14. A passive infra-reddetector according to claim 13 and wherein said focusing elementcomprises at least one of a reflective element, a refractive element, adiffractive element and a cylindrical optical element.
 15. A passiveinfra-red detector according to claim 1 and wherein said signalprocessing circuitry is operative to note a sequence of receipt of saidoutput signals by said at least three sub-detectors and to providemotion direction output based on said sequence.
 16. A passive infra-reddetector according to claim 1 and wherein said signal processingcircuitry is operative to note a sequence of receipt of said outputsignals by said at least three sub-detectors and to provide motion pathoutput information based on said sequence.
 17. A passive infra-reddetector according to claim 1 and wherein said passive infra-reddetector is operative to receive radiation from a field-of-view having afield-of-view divergence angle of at least 45 degrees.
 18. A passiveinfra-red detector according to claim 1 and wherein at least one of saidat least three sub fields-of-view comprises a single coplanarazimuthally distributed detection zone.
 19. A passive infra-red detectoraccording to claim 18 and wherein adjacent ones of said at least threesub fields-of-view are separated by a gap of no more than 30 degrees.20. A passive infra-red detector according to claim 19 and wherein saidgap has an angular extent which is less than or equal to a largestazimuthal angle A-2B between any two adjacent detection zones of saidadjacent ones of said at least three sub fields-of-view.
 21. A passiveinfra-red detector according to claim 1 and wherein at least one of saidat least three sub fields-of-view comprises multiple coplanarazimuthally distributed detection zones.
 22. A passive infra-reddetector according to claim 21 and wherein said azimuthally distributeddetection zones have corresponding divergence angles and said gap has anangular extent which is less than or equal to twice the largest angularextent of said divergence angles of detection zones of said adjacentones of said at least three sub fields-of-view.
 23. A passive infra-reddetector according to claim 1 and wherein at least one of said at leastthree sub fields-of-view comprises a single vertically distributeddetection zone.
 24. A passive infra-red detector according to claim 1and wherein at least one of said at least three sub fields-of-viewcomprises multiple vertically distributed detection zones.
 25. A passiveinfra-red detector according to claim 1 and also comprising a housingformed with an aperture adapted for passage theretbrough of infra-redradiation, wherein said at least three sub fields-of-view intersectgenerally at an intersection region located at said aperture, and saidaperture is generally equal in size to the size of said intersectionregion.
 26. A passive infra-red detector according to claim 25 andwherein a window transparent to infra-red radiation is located adjacentsaid aperture.
 27. A passive infra-red detector according to claim 26and wherein a center of said window is located generally at a center ofsaid aperture.
 28. A passive infra-red detector according to claim 26and wherein said window has a circular cross-section.
 29. A passiveinfra-red detector according to claim 26 and wherein said window isgenerally flat.
 30. A passive infra-red detector according to claim 26and wherein said window is formed of at least one of HDPE, Silicon andGermanium.
 31. A passive infra-red detector according to claim 26 andalso comprising masking detection functionality for providing an alarmoutput upon detection of masking materials obstructing said window. 32.A passive infra-red detector according to claim 26 and also comprising aguard element surrounding said window for providing mechanicalprotection to said window.
 33. A passive infra-red detector comprising:at least three sub-detectors, each operative to receive infra-redradiation from a corresponding one of at least three sub fields-of-view,said at least three sub fields-of-view being substantiallynon-overlapping and being angled with respect to each other; and signalprocessing circuitry, receiving output signals from said at least threesub-detectors and noting time differences between receipt of said outputsignals from adjacent ones of said at least three sub-detectors andproviding a motion detection output in response to receipt of saidoutput signals from said adjacent ones of said at least threesub-detectors having a time difference which is at least within certainpredetermined limits.
 34. A passive infra-red detector according toclaim 33 and wherein said signal processing circuitry is operative tonote a sequence of receipt of said output signals by said at least threesub-detectors and to provide motion direction output based on saidsequence.
 35. A passive infra-red detector according to claim 33 andwherein said signal processing circuitry is operative to note a sequenceof receipt of said output signals by said at least three sub-detectorsand to provide motion path output information based on said sequence.36. A passive infra-red detector according to claim 33 and wherein saidpassive infra-red detector is operative to receive radiation from afield-of-view having a field-of-view divergence angle of at least 45degrees.
 37. A passive infra-red detector according to claim 33 andwherein at least one of said at least three sub fields-of-view comprisesa single coplanar azimuthally distributed detection zone.
 38. A passiveinfra-red detector according to claim 37 and wherein adjacent ones ofsaid at least three sub fields-of-view are separated by a gap of no morethan 30 degrees.
 39. A passive infra-red detector according to claim 38and wherein said gap has an angular extent which is less than or equalto a largest azimuthal angle A-2B between any two adjacent detectionzones of said adjacent ones of said at least three sub fields-of-view.40. A passive infra-red detector according to claim 33 and wherein atleast one of said at least three sub fields-of-view comprises multiplecoplanar azimuthally distributed detection zones.
 41. A passiveinfra-red detector according to claim 40 and wherein said azimuthallydistributed detection zones have corresponding divergence angles andsaid gap has an angular extent which is less than or equal to twice thelargest angular extent of said divergence angles of detection zones ofsaid adjacent ones of said at least three sub fields-of-view.
 42. Apassive infra-red detector according to claim 33 and wherein at leastone of said at least three sub fields-of-view comprises a singlevertically distributed detection zone.
 43. A passive infra-red detectoraccording to claim 33 and wherein at least one of said at least threesub fields-of-view comprises multiple vertically distributed detectionzones.
 44. A passive infra-red detector according to claim 33 and alsocomprising a housing formed with an aperture adapted for passagetherethrough of infra-red radiation, wherein said at least three subfields-of-view intersect generally at an intersection region located atsaid aperture, and said aperture is generally equal in size to the sizeof said intersection region.
 45. A passive infra-red detector accordingto claim 44 and wherein a window transparent to infra-red radiation islocated adjacent said aperture.
 46. A passive infra-red detectoraccording to claim 45 and wherein a center of said window is locatedgenerally at a center of said aperture.
 47. A passive infra-red detectoraccording to claim 45 and wherein said window has a circularcross-section.
 48. A passive infra-red detector according to claim 45and wherein said window is generally flat.
 49. A passive infra-reddetector according to claim 45 and wherein said window is formed of atleast one of HDPE, Silicon and Germanium.
 50. A passive infra-reddetector according to claim 45 and also comprising masking detectionfunctionality for providing an alarm output upon detection of maskingmaterials obstructing said window.
 51. A passive infra-red detectoraccording to claim 45 and also comprising a guard element surroundingsaid window for providing mechanical protection to said window.
 52. Apassive infra-red detector comprising: at least three sub-detectors,each operative to receive infra-red radiation from a corresponding oneof at least three sub fields-of-view, said at least three subfields-of-view being angled with respect to each other; and signalprocessing circuitry, receiving output signals from at least twoadjacent ones of said at least three sub-detectors, noting timedurations of said output signals and providing a motion detection outputin response to receipt of said output signals from said at least twoadjacent ones of said at least three sub-detectors having respectivetime durations, the ratio of which is within predetermined limits.
 53. Apassive infra-red detector according to claim 52 and wherein said atleast three sub fields-of-view are substantially non-overlapping.
 54. Apassive infra-red detector according to claim 52 and wherein said ratiois within the range of 0.5 to 2.0.
 55. A passive infra-red detectoraccording to claim 52 and wherein said signal processing circuitry isoperative to note a sequence of receipt of said output signals by saidat least three sub-detectors and to provide motion direction outputbased on said sequence.
 56. A passive infra-red detector according toclaim 52 and wherein said signal processing circuitry is operative tonote a sequence of receipt of said output signals by said at least threesub-detectors and to provide motion path output information based onsaid sequence.
 57. A passive infra-red detector according to claim 52and wherein said passive infra-red detector is operative to receiveradiation from a field-of-view having a field-of-view divergence angleof at least 45 degrees.
 58. A passive infra-red detector according toclaim 52 and wherein at least one of said at least three subfields-of-view comprises a single coplanar azimuthally distributeddetection zone.
 59. A passive infra-red detector according to claim 58and wherein adjacent ones of said at least three sub fields-of-view areseparated by a gap of no more than 30 degrees.
 60. A passive infra-reddetector according to claim 59 and wherein said gap has an angularextent which is less than or equal to a largest azimuthal angle A-2Bbetween any two adjacent detection zones of said adjacent ones of saidat least three sub fields-of-view.
 61. A passive infra-red detectoraccording to claim 52 and wherein at least one of said at least threesub fields-of-view comprises multiple coplanar azimuthally distributeddetection zones.
 62. A passive infra-red detector according to claim 61and wherein said azimuthally distributed detection zones havecorresponding divergence angles and said gap has an angular extent whichis less than or equal to twice the largest angular extent of saiddivergence angles of detection zones of said adjacent ones of said atleast three sub fields-of-view.
 63. A passive infra-red detectoraccording to claim 52 and wherein at least one of said at least threesub fields-of-view comprises a single vertically distributed detectionzone.
 64. A passive infra-red detector according to claim 52 and whereinat least one of said at least three sub fields-of-view comprisesmultiple vertically distributed detection zones.
 65. A passive infra-reddetector according to claim 52 and also comprising a housing formed withan aperture adapted for passage therethrough of infra-red radiation,wherein said at least three sub fields-of-view intersect generally at anintersection region located at said aperture, and said aperture isgenerally equal in size to the size of said intersection region.
 66. Apassive infra-red detector according to claim 65 and wherein a windowtransparent to infra-red radiation is located adjacent said aperture.67. A passive infra-red detector according to claim 66 and wherein acenter of said window is located generally at a center of said aperture.68. A passive infra-red detector according to claim 66 and wherein saidwindow has a circular cross-section.
 69. A passive infra-red detectoraccording to claim 66 and wherein said window is generally flat.
 70. Apassive infra-red detector according to claim 66 and wherein said windowis formed of at least one of HDPE, Silicon and Germanium.
 71. A passiveinfra-red detector according to claim 66 and also comprising maskingdetection functionality for providing an alarm output upon detection ofmasking materials obstructing said window.
 72. A passive infra-reddetector according to claim 66 and also comprising a guard elementsurrounding said window for providing mechanical protection to saidwindow.
 73. A passive infra-red detector comprising: at least threesub-detectors, each operative to receive infra-red radiation from acorresponding one of at least three sub fields-of-view, said at leastthree sub fields-of-view being angled with respect to each other; andsignal processing circuitry, receiving output signals from at least twoadjacent ones of said at least three sub-detectors, noting timedifferences between receipt of said output signals and time durations ofsaid output signals and providing a motion detection output in responseto receipt of said output signals from at least two adjacent ones ofsaid at least three sub-detectors having respective time durations and atime difference therebetween, said time durations and said timedifference therebetween having a time relationship therebetween whichmeets at least one predetermined criterion.
 74. A passive infra-reddetector according to claim 73 and wherein said at least three subfields-of-view are substantially non-overlapping.
 75. A passiveinfra-red detector according to claim 73 and wherein said at least onepredetermined criterion comprises whether a ratio between said limedifference and at least one of said time durations lies within apredetermined range of values.
 76. A passive infra-red detectoraccording to claim 75 and wherein said predetermined range of values isbased at least in part on divergence angles of at least two zones of twodifferent ones of said at least three sub fields-of-view correspondingto said at least two adjacent ones of said at least three sub-detectors.77. A passive infra-red detector according to claim 75 and wherein saidpredetermined range of values is based at least in part on an anglebetween at least two zones of two different ones of said at least threesub fields-of-view corresponding to said at least two adjacent ones ofsaid at least three sub-detectors.
 78. A passive infra-red detectoraccording to claim 73 and wherein said at least one predeterminedcriterion comprises whether ratios between said time difference and eachof said time durations lie within a predetermined range of values.
 79. Apassive infra-red detector according to claim 73 and wherein said signalprocessing circuitry is operative to note a sequence of receipt of saidoutput signals by said at least three sub-detectors and to providemotion direction output based on said sequence.
 80. A passive infra-reddetector according to claim 73 and wherein said signal processingcircuitry is operative to note a sequence of receipt of said outputsignals by said at least three sub-detectors and to provide motion pathoutput information based on said sequence.
 81. A passive infra-reddetector according to claim 73 and wherein said passive infra-reddetector is operative to receive radiation from a field-of-view having afield-of-view divergence angle of at least 45 degrees.
 82. A passiveinfra-red detector according to claim 73 and wherein at least one ofsaid at least three sub fields-of-view comprises a single coplanarazimuthally distributed detection zone.
 83. A passive infra-red detectoraccording to claim 82 and wherein adjacent ones of said at least threesub fields-of-view are separated by a gap of no more than 30 degrees.84. A passive infra-red detector according to claim 83 and wherein saidgap has an angular extent which is less than or equal to a largestazimuthal angle A-2B between any two adjacent detection zones of saidadjacent ones of said at least three sub fields-of-view.
 85. A passiveinfra-red detector according to claim 73 and wherein at least one ofsaid at least three sub fields-of-view comprises multiple coplanarazimuthally distributed detection zones.
 86. A passive infra-reddetector according to claim 73 and wherein said azimuthally distributeddetection zones have corresponding divergence angles and said gap has anangular extent which is less than or equal to twice the largest angularextent of said divergence angles of detection zones of said adjacentones of said at least three sub fields-of-view.
 87. A passive infra-reddetector according to claim 73 and wherein at least one of said at leastthree sub fields-of-view comprises a single vertically distributeddetection zone.
 88. A passive infra-red detector according to claim 73and wherein at least one of said at least three sub fields-of-viewcomprises multiple vertically distributed detection zones.
 89. A passiveinfra-red detector according to claim 73 and also comprising a housingformed with an aperture adapted for passage therethrough of infra-redradiation, wherein said at least three sub fields-of-view intersectgenerally at an intersection region located at said aperture, and saidaperture is generally equal in size to the size of said intersectionregion.
 90. A passive infra-red detector according to claim 89 andwherein a window transparent to infra-red radiation is located adjacentsaid aperture.
 91. A passive infra-red detector according to claim 90and wherein a center of said window is located generally at a center ofsaid aperture.
 92. A passive infra-red detector according to claim 90and wherein said window has a circular cross-section.
 93. A passiveinfra-red detector according to claim 90 and wherein said window isgenerally flat.
 94. A passive infra-red detector according to claim 90and wherein said window is formed of at least one of HDPE, Silicon andGermanium.
 95. A passive infra-red detector according to claim 90 andalso comprising masking detection functionality for providing an alarmoutput upon detection of masking materials obstructing said window. 96.A passive infra-red detector according to claim 90 and also comprising aguard element surrounding said window for providing mechanicalprotection to said window.
 97. A passive infra-red detector comprising:at least two sub-detectors each operative to receive infra-red radiationfrom a corresponding one of at least two sub fields-of-view; and signalprocessing circuitry, receiving output signals from said at least twosub-detectors and noting time relationships of said output signals fromsaid at least two sub-detectors and providing a motion detection outputin response to receipt of said output signals from said at least twosub-detectors having a time relationship which meets at least onepredetermined criterion, at least one of said at least one predeterminedcriterion being time duration of at least one of said output signals.98. A passive infra-red detector according to claim 97 and wherein twoof said at least two sub-detectors have substantial horizontalseparation therebetween.
 99. A passive infra-red detector according toclaim 98 and wherein said at least one predetermined criterion is basedat least in part on the extent of said substantial horizontalseparation.
 100. A passive infra-red detector according to claim 97 andwherein said at least two sub-detectors are angled with respect to eachother by a horizontal separation angle and said at least onepredetermined criterion is based at least in part on the extent of saidhorizontal separation angle.
 101. A passive infra-red detector accordingto claim 100 and wherein said signal processing circuitry utilizes saidtime relationships of said output signals from said at least twosub-detectors to compute a distance from the detector of an intrudergenerating said output signals and provides said motion detection outputif said distance is within a predetermined distance range.
 102. Apassive infra-red detector according to claim 101 and wherein saidsignal processing circuitry utilizes the extent of at least one of saidsubstantial horizontal separation between said at least twosub-detectors; said horizontal separation angle between said at leasttwo sub fields-of-view and a divergence angle of at least one detectionzone of at least one of said at least two sub fields-of-view to computesaid distance and provides said motion detection output if said distanceis within said predetermined distance range.
 103. A passive infra-reddetector according to claim 97 and wherein each of said at least two subfields-of-view includes at least one detection zone which diverges by acorresponding horizontal divergence angle and said at least onepredetermined criterion is based at least in part on the extent of saidhorizontal divergence angles.
 104. A passive infra-red detectoraccording to claim 97 and wherein said at least one predeterminedcriterion comprises at least one of: whether a time duration of at leastone of said output signals lies within a predetermined range of values;whether a time duration between receipt of a first output signal from afirst one of said at least two sub-detectors and receipt of a secondoutput signal from a second one of said at least two sub-detectors lieswithin a predetermined range of values; whether a ratio of a first timeduration of said first output signal and a second time duration of saidsecond output signal lies within a predetermined range of values;whether a ratio of said first time duration of said first output signaland said time duration between receipt of a first output signal from afirst one of said at least two sub-detectors and receipt of a secondoutput signal from a second one of said at least two sub-detectors lieswithin a predetermined range of values; and whether a ratio of saidsecond time duration of said second output signal and said time durationbetween receipt of a first output signal from a first one of said atleast two sub-detectors and receipt of a second output signal from asecond one of said at least two sub-detectors lies within apredetermined range of values.
 105. A passive infra-red detectoraccording to claim 97 and wherein said signal processing circuitryutilizes said time relationships of said output signals from said atleast two sub-detectors to compute a speed of motion of an intrudergenerating said output signals and provides said motion detection outputif said speed of motion is within a predetermined speed range.
 106. Apassive infra-red detector according to claim 105 and wherein saidpredetermined speed range is between 0.1 to 3 meters per second.
 107. Apassive infra-red detector according to claim 97 and wherein said signalprocessing circuitry utilizes said time relationships of said outputsignals from said at least two sub-detectors to compute a ratiorepresenting an extent of change in a speed of motion of an intrudergenerating said output signals of said at least two sub-detectors andprovides said motion detection output if said ratio, representing saidextent of change in said speed of motion of said intruder, is within apredetermined ratio range.
 108. A passive infra-red detector accordingto claim 107 and wherein said predetermined ratio range is within atleast one of the ranges 0.7 to 1.5 and 0.8 to 1.3.
 109. A passiveinfra-red detector according to claim 97 and wherein said signalprocessing circuitry utilizes said time relationships of said outputsignals from said at least two sub-detectors to compute a ratio(t₁/t₂)/(Z₀/t/K) representing an extent of change in a speed of motionof an intruder generating said output signals of said at least twosub-detectors and provides said motion detection output if said ratio(t₁/t₂)/(Z₀/t/K) is within a predetermined ratio range, wherein K isdefined as tan(A/2) /tan(B), A is defined as the angle between centersof said at least two sub fields-of-view, B is defined as half the anglebetween the edges of each of said at least two sub fields-of-veiw, t1/t2is defined as the ratio of respective positive and negative peaks ofsaid output signals from respective ones of said at least twosub-detectors, Z₀ is defined as the period of time in which an intrudertraverses the distance between said at least two sub fields-of-view at apredetermined distance from said detector less the distance betweencenters of said at least two sub fields-of-view at said detector, and tis defined as the average of t1 and t2.
 110. A passive infra-reddetector according to claim 97 and wherein at least one of said at leasttwo sub fields-of-view comprises a curtain-like sub field-of-view. 111.A radiation detector according to claim 110 and wherein saidcurtain-like sub field-of-view extends generally through 90 degrees.112. A radiation detector according to claim 111 and wherein saidcurtain-like sub field-of-view extends generally through 90 degrees fromthe vertical to the horizontal.
 113. A passive infra-red detectoraccording to claim 97 and wherein at least one of said at least two subfields-of-view comprises a non-curtain like sub field-of-view.
 114. Apassive infra-red detector according to claim 97 and wherein at leastone of said at least two sub-detectors includes a single element sensor.115. A passive infra-red detector according to claim 97 and wherein atleast one of said at least two sub-detectors includes a multiple elementsensor.
 116. A passive infra-red detector according to claim 97 andwherein said signal processing circuitry also includes a traversal logicfunctionality, which provides an alarm enabling signal based at least inpart on a direction of traversal of said at least two subfields-of-view, and provides said motion detection output based at leastin part on said alarm enabling signal.
 117. A passive infra-red detectoraccording to claim 116 and wherein said traversal logic functionalityprovides said alarm enabling signal if at least one of said at least twosub fields-of-view was traversed.
 118. A passive infra-red detectoraccording to claim 116 and wherein said traversal logic functionalityprovides said alarm enabling signal if at least two of said at least twosub fields-of-view were traversed.
 119. A passive infra-red detectoraccording to claim 118 and wherein said traversal logic functionalityprovides said alarm enabling signal if at least two of said at least twosub fields-of-view were traversed in a first direction and were nottraversed in a second direction, generally opposite to said firstdirection.
 120. A passive infra-red detector according to claim 116 andwherein said traversal logic functionality provides said alarm enablingsignal if at least two of said at least two sub fields-of-view weretraversed in a first direction at least a predetermined time followingtraversal of said at least two sub fields-of-view in a second direction,generally opposite to said first direction.